Minecraft version(s)

1.16.5

Minecraft version details

No response

Mod loader

Forge

Mod loader version

Forge-36.2.1

Fabric API version

No response

In what environment did the problem occur?

My singleplayer world

What went wrong? (Crash logs don't go here)

When you resize yourself smaller your hitbox won't collide with the ceiling properly. I'm not sure about being bigger.

Full list of installed mods

Just this one.

Did the problem cause the game to crash?

No.

Full crash report contents (if you experienced a crash)

I'm unable to reproduce this issue. Can you provide some more info, e.g. steps to reproduce, or images, or a video, etc?
Does this still occur for you in Pehkui 3.1.0?
Confirmed in 3.1.0.