In the original games the engine differentiates from 2 different issues when trying to leave an object on an impossible place.
Place is always unreachable: red "X"
Place currently unreachable (roofs and upper floors, other side of mountain ranges...): BG: red "BLOCKED" / SI: red "CAN'T GET THERE"
But with Exult the "BLOCKED"/"CAN'T GET THERE" messages seem to be missing AT LEAST in the case of roof tops and upper floors (it works in the case of water and maybe others).
from our old SF tracker https://sourceforge.net/p/exult/bugs/1937/