3JT, with a 5.1 setup using side surrounds but not back surrounds it's a good idea to place the side speakers slightly farther back than the sitting position, if possible. With wide dispersion speakers such as the QS8s there's little difference between mounting them on the side walls very close to the back wall or on the back wall very close to the side walls, if you're sitting very close to the back wall. Since you say that it's more convenient for you, put them on the side walls maybe 1' from the back wall.
