Hello again, James. Much depends on your room, of course. In my situation I'm using my 12" HPD's in a room 16' X 34' w/cathedral ceilings.
My speakers are about 54" from the wall, positioned along the short wall, driving the long part of the room. They are toed-in so the centers are aimed so they meet at my shoulders, my listening position is 108" from the speaker fronts. Speakers are 54" from the side walls, measured to the center of each driver.
Tannoys have been used in many different room conditions and configurations successfully, feel free to experiment.
Regards,
Dan