Using the normally inaccessible debug feature to view blocks' collision bounds, i was messing around with pistons when i noticed that west-facing pistons' heads are split up into several unnecessary pieces. Most pistons' collision has 3 parts: the base, the shaft, and the head, but on wet pistons, the head is sliced up into multiple pieces. This can also be demonstrated by lining the bottom of your feet up with the bottom of the shaft of the piston in spectator mode, then going into survival mode to cancel flight. you will land on one of these pieces at y+0.375, instead of falling through like you would on any other piston.