Lapierre: I have panels at the primary reflection point. Not sure where the secondary reflection point is.
Philjolet: I'm assuming you're talking about the bass traps. I have tubes in the rear corners. I don't think the panels could go behind me. However, you did inspire me to play with the position behind the speakers. Pulling them out from the corner (about half way between the corner and the speakers) seems to be the magic spot, which also happens to be about where the bass mode seemed to be located. I find it to be somewhat counter-intuitive that by absorbing bass at the mode, it would have the effect of tightening the bass at the listening position, but seems like that's how it works. In fact, now that I think about it, I guess that's the whole point. Duh.
Thanks for the suggestions.