If u find it wandering stick tape to the tile 1st
again I ask can you not put it in the ceiling.
The reason I say this, a wall mounted extractor fan is very rarely hard up against the ceiling and usually a few inches away. What then happens is all the steam doesn't get sucked out and you end up with a mouldy ceiling.
I ceiling fitted fan solves this problem
it also solves the problem of having to drill a 4" hole from the inside which causes masses of dust and no broken tiles, it is also easier to get power to it.
good luck whichever you choose