doubt in faster rcnn config

[zhaoxin111]

According to the logic of the _bbox_forward method, only the first four feature layers are responsible for bbox feature representation. I check the config of faster rcnn in detectron2, all 5 feature maps are responsible for the proposal feature representation. Why mmdet only use 4 feature maps in bbox_roi_extractor?

[ZwwWayne]

The five feature maps are used for proposal generation. But for RoI feature extraction we only use the 4 feature maps.

[zhaoxin111]

Why？