pip install -r https://raw.githubusercontent.com/ultralytics/yolov5/master/requirements.txt

Results:

cascade detector

left + right ear: Average IOU: 30.35%

v2

Resized to 416x416 (center crop)

v2 (round): Average IOU: 87.74%
v2 (floor): Average IOU: 85.83%
v2 (ceil) : Average IOU: 87.49%

v3

Resized to 416x416 (center crop), blur

v3 (round): Average IOU: 85.53%
v3 (floor): Average IOU: 84.16%
v3 (ceil): Average IOU: 84.82%

v4

Resized to 416x416

v4 (round): Average IOU: 89.38%