Rear Surround Speaker Distance

I've experimented fairly extensively with different speaker configurations including heights, wides, and rears. Just when I think i have settled on a configuration that "works", I decide to change it which drives my wife nuts. Anyways the only configuration I can't really dial in as well as I would like is 7.2 with rears. I have tried before but haven't really enjoyed it as much and I think it's because of less than optimal placement which brings me to my question. I have read extensively about placement however nobody offers distance from the MLP, only angles. Is there and optimal distance from the MLP? The reason I keep changing my setup is (OCD)or rather my room doesn't really support heights or wides(optimally) I have plenty of space behing the MLP just not sure how far back. Eventually I will just settle down and pick one and I think it will probably be 7.2 with rears if I can get it to work or go back to regular 5.2.

sduarani, the room is 13 X28 and the MLP is roughly 14' from the back wall.

Thanks but I don't think I can accomodate them along the side walls. They have to be behind the couch. I've tried mounting them against the back wall in the corners and facing the LP and I tried them on the back wall equidistant from the side walls and facing forward. Neither of these sounded right. I could try them on stands directly behind the couch at the appropriate angle but they seem like they would be too close.