Nick, assuming that you're talking about a 5.1 setup without the back surround speakers that are present in 7.1, the QS8s should be a little farther back than directly to the side, to lend a little back effect, even though they're side surrounds. Maybe 2' back is fine and don't be too concerned about the exact relationship in degrees. Yes, since your room is relatively narrow, you should position them as close to the side walls as possible.
EAP, welcome. Since you'll be almost up against the back wall, your side surrounds can be mounted on the back wall about 3' above ear level and spread as widely as possible, preferably more than the 1' beyond the edge of the couch that you mention.
