Daphoid, my QS8s are currently flat against the back wall, but they were much better when they were on stands at the sides of the couch. Since you have a more or less ideal place to put your right surround (about where that green painting is?), you only need to worry about the left surround. I think you'll be happier with the sound if you figure out some way to mount that left QS to your left rather than behind you.
How about using a board about 12" high and 16-20" long to mount your QS on, then use a HEAVY duty door hinge (or two) to mount the board to the back wall, allowing the board to be swung out into position for movies and then folded back against the wall for neat storage.
Judging by the size of your bed, it doesn't look like WAF is an issue, eh?
