Tail rotor placement...
Well, there are a number of theories as to which side it should be on. The most affecting factor is not which side it is on, but rather wether the tail rotor blades closest to the main rotor disc (the front one) is going up through the main rotor downwash or down with it. You can see that the UH1, for instance, had it on different sides between models and finally settled for the right side of the boom. I read a bunch of papers on this, but I cannot remember wether it was up or down that was the best solution. The issue of tail boom and vertical stabiliser interference is much less of an issue, as is the position of said items in respect to disturbing air flowing into the rotor or the thrust.
Hope this sheds some light...