[Plane]

I think this might built on uncertainty we have to what happens to matter that was occupying the space that someone Warps into, and vice versa what happens to the space the character used to occupy.

B98 Hyperjump doesn't need to know since you actually travel through intervening spaces.

P89 Tunnel similarly doesn't need to know because you're bending space but not swapping space.

In either case you can just push aside stuff like air molecules or water molecules.

But in an instantaneous swap it makes you wonder:
1) do new-location molecules swap places with your former location?
2) do new location molecules move outward from your centre of mass?

In the first case, if you teleport into a swimming pool, the water level would not rise because the water formerly there is gone, but you would make a splash at your former location.

In the 2nd case, the water level would rise and a vacuum would be briefly left at your former location, until the air molecules filled it in, which would lower the air pressure if it was a sealed room.

Complications would arise in the 2nd case if you were doing stuff like teleporting into a sealed box of water though, because if you're occupying 90% of that box then the water pressure is probably going to rise 10x possibly injuring you or damaging the box.

On the other hand, the 1st case is complicated since you're also teleporting-back some stuff to make way, so some guy teleporting into a volcano would get some free lava attack back where he left.