the spacing there is to keep the chain aligned with the sprocket on the rear wheel. if i were to move the rear driven, it would throw alignment of the chain off, and the chain would rub on the gear itself, and on the tire.
What do you have for spacers on your rear wheel? Maybe those are messed up making everything else out of line
Also is your sprocket bolted sirectly to the wheel with no spacers or washers?