I would imagine that the best compromise is the fenestron system (i.e. rotor inside rear fin). This would allow an unblocked airflow, and allow less drag in foward flight. In this case direction will be less critical, but top rearward will interfere less with the main vortex I would imagine.
One of the most critical factors is tail rotor height wrt the main blade. Since the main blade has to overcome the side thrust of the tail rotor, any height difference will cause a left down roll torque (since tail rotor is lower). Watch a jet ranger next time it touches down. A virtual dollar says it's left skid first...
Mart