I'd put the speakers on the short height long wall. The upward slope on the ceiling may help first order reflections since it would be more of a tangential interface. Long wall placement also gets you away from the side walls which delays the first reflections thereby helping that problem some as well. If the seat/couch is close to the back wall adsorption directly behind your head (i.e big pillows) helps a ton. My speakers are long wall positioned and the sound stage is significantly wider and more open than a short wall set up.
HELP Which wall of new room to put system on?
I'm probably moving my system into a new room. The room is about 15' wide x 20' long. I will put the system on one of the 15' walls. The room height is 8' except that one wall only goes to 5'4" and begins a gradual slant up to 8'. I would like to get everyone's advice about whether I should put the main system / front speakers on the wall with the slant or on the wall that goes straight up to 8' tall. I'm hoping that, in some way, this will be a sonic advantage. I'm just not sure if the slant should be behind the main front speakers or on the other end of the room from them. By the way, the main front speakers will probably sit about 5' off the wall.