I have a 16' x 14' Theater room. My 4 & 5 diplar surrounds are in the ceiling 3 and 1/2 feet from the rear, and 2 feet in from the sides. The couch is 2 feet from the rear wall, and the large screen (55")TV is on the 16' long wall. The 6 & 7 dipoles are one the rear wall 2 and 1/2 feet from the ceiling, and equidistant from the 4 & 5.
This arrangement is trully fine for 7 channels. All speakers are Monitor Audio Silver's.