While Saitou's suggestion make sense to me, a pure-fluff solution is to say that cubes are very springy, so it's movements cause a brief wave of emptiness at the edges that can be moved through if the tactically-minded warlord is expecting it.
A more oozy option is to say when moving, the cube gathers its ooze from around the edges towards the new center, briefly leaving space to move around.
A more oozy option is to say when moving, the cube gathers its ooze from around the edges towards the new center, briefly leaving space to move around.