Hitbox probably should stay as the normal size.

Is this while you drag the slider, or when you exit the BPI menu?

Also the hitbox size difference is negligible.

Is this while you drag the slider, or when you exit the BPI menu?

Also the hitbox size difference is negligible.

When you exit the menu after changing your size.
But since the hitbox is only different on the client, the server will teleport you back if you try to fit under spaces that you wouldn't be able to normally.

I was not able to replicate this bug. Please provide a video showcasing how you caused this.

When I get a chance later I will.

@LtxProgrammer
Okay, this doesn't seem to a hitbox size related issue, it appears to be something wrong with entity collision/hitbox with any transfurred player in general.
If moving against a wall, the camera and player will stutter (also why is the latex human hitbox larger? Can't fit under a slab).

I've determined the stuttering is from a compatibility issue. Yird had provided me with the list of mods used in the videon

- LazyDFU [0.1.3]
- Ferrite Core [4.2.2]
- WorldEdit [7.2.10+1742f98]
- Alternate Current [NONE]
- Saturn [0.1.5]
- TexTrue's Embeddium Options [0.1.1+mc1.18.2]
- Changed: Minecraft Mod [0.13.1]
- Chat Heads [0.6.1]
- Make Bubbles Pop [${file.jarVersion}-forge]
- ModernFix [5.15.0+mc1.18.2]
- Model Gap Fix [1.8]
- ReBlured [1.18.2-1.2.0]
- Roughly Enough Items (REI) [8.3.681]
- Kiwi [6.1.4]
- Cloth Config v4 API [6.5.102]
- Fastload-Reforged [3.4.0]
- Lightspeed [1.18.2-1.1.0]
- Music Duration Reducer [NONE]
- Embeddium [0.3.10+mc1.18.2]
- Bounced [1.18.2-2.1.4]
- Suggestion Tweaker [1.18.2-1.5.1]
- Forgematica [0.1.8-mc1.18.2]
- Kotlin for Forge [NBn3sEQk]
- NotEnoughAnimations [1.7.1]
- Jade [5.3.2]
- ImmediatelyFast Reforged [1.18.2-1.1.10]
- MaFgLib [0.1.9-mc1.18.2]
- MyServerIsCompatible [1.0]
- Catalogue [1.6.2]
- Architectury [4.12.94]
- Configured [2.0.1]
- Better Biome Blend [1.3.5-forge]
- Better Statistics Screen [2.2.2+1.18.2]
- Game Menu Mod Option [1.14.2]
- Raised [3.1.3]
- EntityCulling [1.6.1]
- Xaero's World Map [1.38.1]
- Async Locator [1.18.2-1.1.0]
- Dynamic Music [2.3.1+1.18.2]

Bijimio was able to replicate this bug in the dev environment. He set the BPI size to < 100%, and walked into a wall. I am still unable to replicate it consistently myself.

I think I found it. Bug seems to occur when the player esc's out of the BPI screen. Reviewing the code shows that the BPI packet only sends when the player clicks "Done"