speaker placement help

My room is 13'x18'x11'high. I have my speakers on the short wall 6 feet into the room and about 33 and 1/2 inches into the room from the side walls. The room is rectangular and I have the speakers perfectly symetrical.My question is that should my listening position be an equilateral point from the distance of the speakers or is it OK to have my listening position 1 and 1/2 the distance of the speakers back towards the back wall therefore having my listening position at the back wall as opposed to three feet from the back wall.I've tried both ways and find I get a better bass response with the listening position at the back wall but some say it's good to have distance between your listening position and the back wall and others say it's OK to be at the back wall.Any help would be appreciated!!!