Hi Randy
I've never had much luck with the quick placement formulae because nodes will vary considerably from room to room, so one persons placement doesn't always translate to another's room.
From the pics of your great looking room, I'd say you still have a few challenges finding ideal placement because of its large irregular layout. I had a similar situation with my irregular space until last year when I built another small wall to seal the room. The larger the volume the more difficult it will be for one sub to pressurize the room.
With only one sub your situation may actually work better with the 500 in the corner. FR will be less linear but the overall result could be better depending on your seating position . Generally speaking I've found one-third to one-half distance from a corner works best with one sub if your goal is flatter response. As you move closer to the corner you benefit from more room gain but less linear FR. Given the size of room and layout a second EP500 along the front wall or one on the frontwall and another on a sidewall should really perform well.
Another suggetion would be stay with one 500 and get an SMS-1 to equalize FR at the main seating area. It's graphical display will also help you pinpoint the ideal placement.
