In general I agree with the consensus on asymmetry here, but remember, the point is not the rule but how you apply it. You don't just stay relaxed forever. You fluctuate between states depending on which is beneficial to you at the time. Look at this video of me #-closing a two-set during daygame (you can't hear the sound that well but I want you to see the body language):
http://www.youtube.com/watch?v=9QTkuRVA ... annel_page
When I'm sitting down, most of the time I'm laid back and relaxed, taking up space. But I do lean in at crucial points for specific reasons. It's all about being versatile and timing. Use the right body language at the right times.