Reuben, for 5.1 you want your left/right surrounds to be to the left/right of your primary listening area, not behind you. The term Rears should be used for the actual rear channels for 7.1 setups. Here is a link to one of the articles from Alan at Axiom describing placement. Sometimes room size/limitations require people to place the surrounds behind them a bit, but you still want them spaced out to the sides.
http://www.axiomaudio.com/archives/home_theater_layout.html
Standard DD 5.1, PLII
Standard DD 7.1 setup
DD 5.1 Corner room setup.
