Good question. You have to put the fuel tank in a logical place and make sure the engine/prop when running is going to make pushing forces. I believe the reason that most airplanes use tractor engines is that the airflow is cleaner and it allows the power transfer into thrust to be better than a pusher. Think of the air going around a fuselage with bumps, etc and the effect of wing lift getting in the mess and the flow into a pusher prop is pretty messed up. It will work but not as good as a tractor.

The thrust over the elevators would make that surface more effective but that alone isn't worth the propulsion loss. You can just make the elevator bigger and regain the same effectiveness. Certainly in the long run the location of just the thrust component from front to rear doesn't effect the airplane adversly. A modern jet has the thrust at the rear and works fine.

This would be a fun thing to investigate with a small foamy type of airplane. Build a tractor/pusher configuration and compare the results flying on each one and then both.