Update:
I finally got around to sourcing some acoustic fiberglass and built myself some 2' x 4' x 6" panels for testing. The results were interesting.
The most notable items:
1. when I checked my calibration I noticed that I had lost 2db on my front right speaker. I noticed the side couch was out of place so I moved it back 6" so that it was now 25" from the speaker and got my 2db back.
2. I thougt I would try the two panels on the kitchen table (dining area) about 3.5' from the wall. The result was a graph about the same as putting both panels across the back corner floor to ceiling.
3. All of the positions eliminated the 42Hz hole.
4. I saw a +3db gain in the 22-28Hz area. Didn't think I would see any effect this low.
I am encouraged and will probably pick up another bale of acoustic glass soon.
I will post graphs tomorrow. Gotta get some sleep now.