Thing is, the wheel needs to be big enough or the hamster won`t use it. This is possibly why he makes a nest in it.
Also, if it`s too big for the cage or won`t turn because the level above isn`t allowing that, the cage needs to be adapted so that your wheel fits. Maybe just having one upper shelf would allow better wheel use?
If the wheel fits at the front, it will fit at the back surely? It`s the same space/height?