My HT uses more than half of a 16x40 ft room. My seating area is open to the rear to another room, necessitating the use of in-ceiling 7.1 rear surrounds. I realize that all speakers should be about the same distance from the seating area. Is that distance measured across the floor, or directly to the speaker? In other words, with an 8 ft. ceiling, does the 5 ft distance from the couch to the ceiling count? Also, how far apart should they be mounted? Thanks.