I guess I didnt explain very well. If you have 2 in ceilings set up at opposite sides of a 30' long room in stereo, the stereo mix usually has elements that move across what would normally be a left/right stereo setup. In an in ceiling setup with music, the effect is you just dont hear some parts of the music, or conversely hear them all to well depending on where your seat is. If I think of a 3 piece jazz recording, like Brubeck, it would be wierd to have a sax way over there and a piano way over there. Thats why mono is often used in architectural setups. It isnt distracting and doesnt bias any elements of the sound based on listener location. The goal in a commercial setting is even coverage, not anything to do with stuff we care about, like soundstage.
