My system is also 5.1 and my L-R mains are about 6 feet apart. My problem is the MLP is just too far away, so when "critical listening" of 2.1 is what I'm doing, I move me to just about 7 feet away. Speakers remain pointed dead straight.
Under those conditions, I have got to stop getting up to check if the center speaker is on. It's just unreal how perfect the stereo imaging is that way.