From what I've read the rear speaker placement should be on each side of the listening position, in fact I read that you were better of not having rear speakers at all then to have them behind the listener and aimed forward. I have a fireplace and window to one side and entrance hall on the other so the best place for speakers is on the back wall just behind my sectional (couch). If I'm using the QS4's or QS8's would it be a mistake to mount them on the back wall?