Solid entity collisions don't count for short sneaking and crawling

Steps to Reproduce:

1. Turn on the Short Sneaking/Crawling experiment
2. Place boats leaving a <=1.5 block high gap underneath;
3. Start sneaking (or crawling if needed) and try to go underneath.

Observed Results:
You aren't forced to keep that position and just stand up, pushing all the boats out.

Expected Results:
You keep the pose until you can properly stand without pushing any boats.

Screenshots/Videos attached: Yes

Notes: You can stand on boats, which is why this behavior would be expected.