Player can't be forced to crouch while in fly mode

Steps to Reproduce:

1. Enable the Short Sneak experiment;

2. Place blocks around you to not get pushed out;

3. Enter fly mode;

4. Using a piston, push an upper slab into your standing space.

Observed Results:
The collision and camera stay the same both visually and functionally, despite not having enough space to stand.

Expected Results:
The player gets forced into a sneaking position to accomodate the decreased space.

Screenshots/Videos attached: Yes

Notes: Due to a change made to disallow players from entering and leaving fly mode while being forced to crouch, this issue is made worse and forces the player to destroy the setup in order to get out.