Mob spawning is not using json-defined collision box when checking for obstructions

1. Head Obstruction while spawning

How to reproduce

• Load the attached World in 1.20.10.20 Preview 
• Set the Head level as "Trapdoor" 

Expected result 

No mob spawning except Creepers & Spiders 

Actual result 

All mobs are able to spawn 

 

2. Spider spawn not blocked by buttons 

How to reproduce

• Load the attached World in 1.20.10.20 Preview 
• Set the feet level as "buttons" 

Expected result 

Spiders are unable to spawn (No 3x1x3 area available)

Actual result 

Spiders are still able to spawn 

3. Ghast and magma cube spawn in 2-block high area

How to reproduce

• Find a basalt delta and make a 48 x 2 x 48 stone platform.
• 3 blocks above that make a 48 x 1 x 48 stone roof (so that there are 2 blocks of air between the platform and the roof).
• Fly 24 blocks from the platform.
• Teleport all non-player entities to the void.
• Watch the platform.

Expected result

No ghast or magma spawn in the 2-block high area.

Actual result

Ghast and magma spawn in the 2-block high area. May need to repeat a few times to get ghasts since they have a small cap.