Magnepan MMG Speaker Placement in a Small Room

I just picked up a pair of MMGs and I have a question about speaker placement.  My listening room is very small at 12'x10'.  Right now, I have them setup with the tweeter to the inside and 4' off the back wall.  Anybody got recommendations on the optimal placement between the speakers? When taking measurements, should I measure at the center of the speaker, the outside edge, or inside edge?