Occasionally missing reference arrow line

[jgieseler]

On some occasions, the line of the arrow indicating the reference is missing:

This might be connected to the radial range that is plotted because in the following it is fine:

In addition, if the radial range changes, e.g. by adding Mars or some other further positioned observer, the tip of the arrow changes in size. So it might be better to not define the arrow length & shape in absolute values, but rather fraction of r_max.

Hopefully this also fixes the bug of the missing arrow line.