Bob, I'd definitely try moving them to the front. Along my subwoofer locating journey I placed my subs behind me and hated it. The bass just felt disconnected from the mains and left a large gap. Even switching phases and subwoofer distance in the AVR didn't help. If possible I'd place the PB-12's in a front corner either side by side or on top of eachother for the 6db boost along with the advantage of being placed by two boundaries. That should surely knock your socks off
