diff --git a/four_letter_blocks/block_packer.py b/four_letter_blocks/block_packer.py
index ec81085..7c757a5 100644
--- a/four_letter_blocks/block_packer.py
+++ b/four_letter_blocks/block_packer.py
@@ -54,6 +54,14 @@ def __init__(self,
         if 0 <= min_tries < tries:
             self.stop_tries = tries - min_tries
         self.is_tracing = False
+
+        # True if slots should be filled in random order, otherwise False if
+        # slots should be filled from top to bottom.
+        self.are_slots_shuffled = False
+
+        # True if self.state should be set, even with a partial filling
+        self.are_partials_saved = False
+
         self.fewest_unused: int | None = None
         self.slot_coverage = self.state
 
@@ -100,7 +108,7 @@ def calculate_max_shape_counts(self):
         """
         # noinspection PyUnresolvedReferences
         block_count = (self.state == 0).sum() // 4
-        block_count += 5*7  # Add flexibility to make packing easier.
+        block_count += 7  # Add flexibility to make packing easier.
         multiplier = {'O': 4, 'S': 2, 'Z': 2, 'I': 2}
         shape_names = Block.shape_rotation_names()
         return {shape: math.ceil(multiplier.get(shape[0], 1) * block_count / 28)
@@ -159,7 +167,7 @@ def find_slots(self) -> dict[str, np.ndarray]:
             slot_coverage += shape_coverage
             slots[shape] = usable_slots
         self.slot_coverage = slot_coverage
-        if slot_coverage.all():
+        if self.are_partials_saved or slot_coverage.all():
             return slots
 
         # Some unfilled spaces weren't covered by any usable slots, return empty.
@@ -234,24 +242,27 @@ def create_block(self, block_num):
         block = Block(*squares)
         return block
 
-    def fill(self,
-             shape_counts: typing.Counter[str],
-             are_slots_shuffled: bool = False,
-             are_partials_saved: bool = False) -> bool:
+    def fill(self, shape_counts: typing.Counter[str]) -> bool:
         """ Fill in the current state with the given shapes.
 
         Cycles through the available shapes in shape_counts, and tries them in
         different positions, looking for the fewest rows. Set the current state
         to a filled in copy, not changing the original.
 
+        Slots with least coverage are always filled first. If
+        self.are_slots_shuffled is True, then coverage ties are broken randomly,
+        otherwise ties are filled from top to bottom.
+
+        If self.are_partials_saved is True, then we don't cycle through options,
+        just make the first choice for each slot and return with self.state set.
+
         :param shape_counts: number of blocks of each shape, disables rotation
-            if any of the shapes contain a letter and rotation number
-        :param are_slots_shuffled: True if slots should be filled in random
-            order, otherwise False if slots should be filled from top to bottom.
-        :param are_partials_saved: True if self.state should be set, even with
-            a partial filling
+            if any of the shapes contain a letter and rotation number. Adjusted
+            to remaining counts, if self.are_partials_saved is True.
         :return: True, if successful, otherwise False.
         """
+        are_slots_shuffled = self.are_slots_shuffled
+        are_partials_saved = self.are_partials_saved
         if self.tries == 0:
             self.state = None
             return False
@@ -260,6 +271,9 @@ def fill(self,
         best_state = None
         assert self.state is not None
         start_state = self.state
+        if not sum(shape_counts.values()):
+            # Nothing to add!
+            best_state = start_state
         next_block = self.find_next_block()
         fewest_rows = start_state.shape[0]+1
 
@@ -284,7 +298,6 @@ def fill(self,
                 continue
             # noinspection PyTypeChecker
             shape_scores[shape] = -slot_count / target_count
-        is_filled = False
         for shape, _score in shape_scores.most_common():
             if not is_rotation_allowed:
                 slot_shapes = [shape]
@@ -326,9 +339,7 @@ def fill(self,
                                   f'finished? {is_finished}')
                             print(self.display())
                         if not is_finished and self.tries != 0:
-                            is_filled = self.fill(shape_counts,
-                                             are_slots_shuffled,
-                                             are_partials_saved)
+                            is_filled = self.fill(shape_counts)
                             if not is_filled:
                                 continue
                         used_rows = self.count_filled_rows()
@@ -352,11 +363,9 @@ def fill(self,
             if are_partials_saved:
                 break
             shape_counts[shape] = old_count
-        if is_filled:
-            return True
-        if ((not is_rotation_allowed or best_state is None) and
-                not are_partials_saved):
-            return False
+        # if ((not is_rotation_allowed or best_state is None) and
+        #         not are_partials_saved):
+        #     return False
             # new_state = start_state.copy()
             # # noinspection PyUnboundLocalVariable
             # new_state[target_row, target_col] = 1  # gap
@@ -372,8 +381,8 @@ def fill(self,
             self.state = None
         return False
 
-    def find_next_block(self):
-        used_blocks = np.unique(self.state)
+    def find_next_block(self) -> int:
+        used_blocks = np.unique(self.state)  # type: ignore
         block: int
         for i, block in enumerate(used_blocks[:-1]):
             if block >= self.GAP and used_blocks[i + 1] != block + 1:
@@ -438,9 +447,9 @@ def count_filled_rows(self):
 
     def random_fill(self, shape_counts: typing.Counter[str]):
         """ Randomly place pieces from shape_counts on empty spaces. """
-        self.fill(shape_counts,
-                  are_slots_shuffled=True,
-                  are_partials_saved=False)
+        self.are_slots_shuffled = True
+        self.are_partials_saved = False
+        self.fill(shape_counts)
 
     def flip(self) -> 'BlockPacker':
         assert self.state is not None
diff --git a/four_letter_blocks/double_block_packer.py b/four_letter_blocks/double_block_packer.py
index 4df471a..b66cc05 100644
--- a/four_letter_blocks/double_block_packer.py
+++ b/four_letter_blocks/double_block_packer.py
@@ -97,7 +97,9 @@ def fill(self) -> bool:
             shape_scores[shape] = -slot_count / target_count
 
         start_state1 = packer1.state
+        assert start_state1 is not None
         start_state2 = packer2.state
+        assert start_state2 is not None
         next_block = packer1.find_next_block()
         for shape1, _score in shape_scores.most_common():
             shape2 = flipped_shape_names[shape1]
diff --git a/four_letter_blocks/evo_packer.py b/four_letter_blocks/evo_packer.py
index 760e82f..8f748e0 100644
--- a/four_letter_blocks/evo_packer.py
+++ b/four_letter_blocks/evo_packer.py
@@ -102,7 +102,11 @@ def pair(self, other, pair_params):
             mover2.move(i2, j2)
         packer = BlockPacker(start_state=new_state)
         packer.force_fours = True
-        packer.random_fill(mover1.shape_counts)
+        packer.are_slots_shuffled = True
+        packer.are_partials_saved = True
+        packer.fill(mover1.shape_counts)
+
+        assert packer.state is not None
         return Packing(dict(state=packer.state,
                             shape_counts=mover1.shape_counts,
                             can_rotate=can_rotate,
@@ -117,6 +121,8 @@ def mutate(self, mutate_params) -> None:
         can_rotate: bool = self.value['can_rotate']
         block_packer = BlockPacker(start_state=state)
         block_packer.force_fours = True
+        block_packer.are_partials_saved = True
+        block_packer.are_slots_shuffled = True
         grid_size = state.shape[0]
         gaps = np.argwhere(state == 0)
         if gaps.size > 0:
@@ -149,8 +155,9 @@ def mutate(self, mutate_params) -> None:
             if remove_count == 0:
                 break
 
-        block_packer.random_fill(shape_counts)
+        block_packer.fill(shape_counts)
 
+        assert block_packer.state is not None
         self.value = dict(state=block_packer.state,
                           shape_counts=shape_counts,
                           can_rotate=can_rotate)
@@ -161,7 +168,11 @@ def _random_init(self, init_params: dict):
         can_rotate = all(len(shape) == 1 for shape in shape_counts)
         block_packer = BlockPacker(start_state=start_state)
         block_packer.force_fours = True
-        block_packer.random_fill(shape_counts)
+        block_packer.are_slots_shuffled = True
+        block_packer.are_partials_saved = True
+        block_packer.fill(shape_counts)
+
+        assert block_packer.state is not None
         return dict(state=block_packer.state,
                     shape_counts=shape_counts,
                     can_rotate=can_rotate)
@@ -270,6 +281,7 @@ def __init__(self,
                          start_state)
         self.is_logging = False
         self.epochs = 100
+        self.pool_size = 1000
         self.current_epoch = 0
         self.shape_counts: typing.Counter[str] = Counter()
         self.evo: Evolution | None = None
@@ -287,10 +299,10 @@ def setup(self,
         fitness_calculator.summaries.clear()
 
         self.evo = Evolution(
-            pool_size=1000,
+            pool_size=self.pool_size,
             fitness=fitness_calculator.calculate,
             individual_class=Packing,
-            n_offsprings=200,
+            n_offsprings=self.pool_size // 5,
             pair_params=None,
             mutate_params=None,
             init_params=init_params,
diff --git a/four_letter_blocks/puzzle_set.py b/four_letter_blocks/puzzle_set.py
index f1427bd..0727ef0 100644
--- a/four_letter_blocks/puzzle_set.py
+++ b/four_letter_blocks/puzzle_set.py
@@ -26,7 +26,8 @@ def __init__(self,
             self.block_packer = block_packer
         else:
             self.block_packer = BlockPacker(16, 20,  # Game Crafter cutout size
-                                            tries=10_000)
+                                            tries=10_000,
+                                            min_tries=1)
         self.front_blocks: typing.Dict[
             str,
             typing.List[Block | None]] = defaultdict(list)
diff --git a/tests/test_block_packer.py b/tests/test_block_packer.py
index 2511e45..3f38e26 100644
--- a/tests/test_block_packer.py
+++ b/tests/test_block_packer.py
@@ -121,8 +121,8 @@ def test_fill_two_blocks():
     width, height = 5, 4
     shape_counts = Counter('LO')
     expected_display = dedent("""\
-        ..ABB
-        AAABB
+        AA..B
+        AABBB
         .....
         .....""")
     packer = BlockPacker(width, height)
@@ -135,8 +135,8 @@ def test_fill_two_blocks_force_fours():
     width, height = 5, 4
     shape_counts = Counter('LO')
     expected_display = dedent("""\
-        AAABB
-        A..BB
+        AABBB
+        AAB..
         .....
         .....""")
     packer = BlockPacker(width, height)
@@ -196,7 +196,7 @@ def test_no_rotations_needs_gap():
     width = height = 5
     shape_counts = Counter(('O', 'J3', 'O'))
     expected_display = dedent("""\
-        AA#CC
+        AA.CC
         AABCC
         ..BBB
         .....
@@ -217,7 +217,9 @@ def test_random_fill():
             .....
             ..##.""")
         packer = BlockPacker(start_text=start_text)
-        packer.random_fill(shape_counts)
+        packer.are_slots_shuffled = True
+        packer.are_partials_saved = True
+        packer.fill(shape_counts)
 
         assert 1 <= shape_counts['O'] <= 3
 
@@ -231,8 +233,10 @@ def test_random_fill_lower_numbers():
             ..#..
             ..DDD
             ..##D""")
-        packer = BlockPacker(start_text=start_text)
-        packer.random_fill(shape_counts)
+        packer = BlockPacker(start_text=start_text, tries=100, min_tries=1)
+        packer.are_slots_shuffled = True
+        packer.are_partials_saved = True
+        packer.fill(shape_counts)
 
         assert 2 <= shape_counts['O'] <= 3
         assert packer.state.max() == 5
@@ -245,7 +249,9 @@ def test_random_fill_tries_multiple_shapes():
             AA...B
             AA.BBB""")
         packer = BlockPacker(start_text=start_text)
-        packer.random_fill(shape_counts)
+        packer.are_slots_shuffled = True
+        packer.are_partials_saved = True
+        packer.fill(shape_counts)
 
         assert shape_counts['L'] == 0
 
@@ -254,7 +260,9 @@ def test_random_fill_no_gaps():
     for _ in range(100):
         shape_counts = Counter({'O': 1})
         packer = BlockPacker(2, 2)
-        packer.random_fill(shape_counts)
+        packer.are_slots_shuffled = True
+        packer.are_partials_saved = True
+        packer.fill(shape_counts)
 
         assert shape_counts['O'] == 0
         assert packer.state.max() == 2
@@ -356,10 +364,10 @@ def test_fill_with_split_row():
         AA.
         AA.
         ...
-        BBB
-        .B.
-        CC.
-        CC.""")
+        BB.
+        BB.
+        CCC
+        .C.""")
     packer = BlockPacker(width, height, split_row=3, tries=100)
     packer.fill(shape_counts)
 
@@ -375,7 +383,7 @@ def test_fill_overflow():
 
     assert len(packer.positions['O']) == 254
 
-    shape_counts['O'] += 1
+    shape_counts = Counter({'O': 255})
     packer = BlockPacker(256, 4, tries=500)
     with pytest.raises(ValueError, match='Maximum 254 blocks in packer.'):
         packer.fill(shape_counts)
@@ -490,8 +498,9 @@ def test_shape_counts_7x7():
         .......
         ...#...
         #.....#"""))
-    expected_shape_counts = {name: 1 for name in Block.shape_names()}
-    expected_shape_counts['O'] = 2
+    expected_shape_counts = {
+        name: 3 if name == 'O' else 2 if name[0] in 'ISZ' else 1
+        for name in Block.shape_rotation_names()}
 
     shape_counts = packer.calculate_max_shape_counts()
 
@@ -509,11 +518,9 @@ def test_shape_counts_9x9():
         .........
         ...#.....
         ...#....."""))
-    expected_shape_counts = {name: 1 for name in Block.shape_names()}
-    expected_shape_counts['O'] = 3
-    for name in expected_shape_counts:
-        if name[0] in 'ISZ':
-            expected_shape_counts[name] = 2
+    expected_shape_counts = {
+        name: 4 if name == 'O' else 2 if name[0] in 'ISZ' else 1
+        for name in Block.shape_rotation_names()}
 
     shape_counts = packer.calculate_max_shape_counts()
 
diff --git a/tests/test_evo_packer.py b/tests/test_evo_packer.py
index 190c33d..7727cac 100644
--- a/tests/test_evo_packer.py
+++ b/tests/test_evo_packer.py
@@ -23,8 +23,10 @@ def test_no_rotations():
         DA#EC
         DEEEC
         DD##C""")
-    packer = EvoPacker(start_text=start_text)
+    packer = EvoPacker(start_text=start_text, tries=100, min_tries=1)
     packer.is_logging = False
+    packer.epochs = 2
+    packer.pool_size = 100
 
     is_filled = packer.fill(shape_counts)
     packer.sort_blocks()
diff --git a/tests/test_puzzle_pair.py b/tests/test_puzzle_pair.py
index fc48ab6..419f8c0 100644
--- a/tests/test_puzzle_pair.py
+++ b/tests/test_puzzle_pair.py
@@ -497,9 +497,8 @@ def test_pack_greetings():
                              min_tries=1)
         back_shapes = packer.calculate_max_shape_counts()
         packer.force_fours = True
-        packer.fill(back_shapes,
-                    are_slots_shuffled=True,
-                    are_partials_saved=False)
+        packer.are_slots_shuffled = True
+        packer.fill(back_shapes)
         if not packer.is_full:
             print('First packer failed.')
             continue
@@ -515,9 +514,8 @@ def test_pack_greetings():
                               tries=1000,
                               min_tries=1)
         packer2.force_fours = True
-        packer2.fill(target_shapes,
-                     are_partials_saved=False,
-                     are_slots_shuffled=True)
+        packer2.are_slots_shuffled = True
+        packer2.fill(target_shapes)
         packer.sort_blocks()
         packer2.sort_blocks()
         display1 = packer.display()
diff --git a/tests/test_puzzle_set.py b/tests/test_puzzle_set.py
index dede4c6..c44c293 100644
--- a/tests/test_puzzle_set.py
+++ b/tests/test_puzzle_set.py
@@ -304,18 +304,18 @@ def test_draw_packed(pixmap_differ: PixmapDiffer):
 
         puzzle_set1.square_size = 20
         blocks = puzzle1.blocks
-        blocks[0].set_display(270, 10, 0)
-        blocks[1].set_display(170, 30, 0)
-        blocks[2].set_display(50, 10, 0)
-        blocks[3].set_display(10, 70, 0)
-        blocks[4].set_display(30, 70, 0)
+        blocks[0].set_display(250, 10, 0)
+        blocks[1].set_display(230, 70, 0)
+        blocks[2].set_display(110, 30, 0)
+        blocks[3].set_display(10, 10, 0)
+        blocks[4].set_display(70, 10, 2)
 
         blocks = puzzle2.blocks
-        blocks[0].set_display(70, 50, 0)
-        blocks[1].set_display(70, 90, 1)
+        blocks[0].set_display(90, 90, 0)
+        blocks[1].set_display(10, 50, 0)
         blocks[2].set_display(170, 10, 0)
-        blocks[3].set_display(250, 70, 0)
-        blocks[4].set_display(230, 10, 0)
+        blocks[3].set_display(210, 10, 2)
+        blocks[4].set_display(170, 30, 0)
 
         for block in puzzle1.blocks + puzzle2.blocks:
             block.draw(expected, is_packed=True)
@@ -334,11 +334,12 @@ def test_draw_cuts(pixmap_differ: PixmapDiffer):
             180,
             'test_puzzle_draw_cuts') as (actual, expected):
         block_text = dedent("""\
-            #ABCCCC
-            #ABBBDD
-            AAEEDDE
-            F#EEGGE
-            FFFGGEE
+            AABCCDD
+            AABCDDE
+            FBBCGGE
+            F##HGEE
+            F##HGII
+            F#HHII#
         """)
         puzzle3 = Puzzle.parse_sections('',
                                         block_text,