I have mixed feelings on my room treatments/advice...My room is L-shaped with a sitting area to the right of the HT portion and bar/bathroom/stairs next to that. Still under construction for a bit, so forgive mess in pics.
I was instructed to place four 244 panels on the left wall which covered FRP for L,C,R,and SR for both back-row-center MLP and front-row-center SLP. Also placed tri-traps in the back corner and 3 monster traps with range-limiter on back wall. It wasn't recommended, but I'm placing six 242 panels on the ceiling to cover the FRP for both middle seats as well. I was really surprised they didn't want me to put any diffusion or scatter plates in the room whatsoever.
The front was completed prior to ordering and I had elected to run with CertainTeed anti-reflective ceiling tiles on the wall with the cheap/ineffective foam bass-traps in the corner...I know it's less than ideal material, but it works great with AT screen reducing reflectivity to less than 3% with an NRC of .75-.90 (I know NRC is kind of irrelevant). It also quieted the front of the room to an extreme making claps ring with a nasty ping in the back of the HT.
After installing the GIK panels, the excellent sound-stage and imaging become significantly wider and deeper. I was blown away with music tests. My speakers were not highly localizable, but they disappeared even more. My bass extension is flat down to 12Hz up to about 28hz F3.
Then I made the mistake of running REW for my first time and noticed that Audyssey and/or the room was giving me some big dips at around 28 and 90Hz with a big mode at about 30-35hz. It also decided it wanted to cross my 80Hz F3 side surrounds at 200hz. I listened to a bunch of movie scenes that I'm intimately familiar with. I just feel like the mid-range or upper LF is missing the "pop" and "punch" now during action/fighting scenes. It also seemed to me that I could now hear reflections off the ceiling which were non-existent before. I find that instead of running movies at reference, I sometimes want to turn it 2-3 db above. Dialogue hasn't really suffered but maybe 5-10% of the time I wonder if it has, hence the increase above reference (though that could just be a quiet scene in the movie).
So maybe I'm conditioned to hearing all the reflections and non-linearities, thus expecting exaggerated FR in certain ranges. Maybe it's the placebo effect and seeing the REW graph below 200Hz, and turning the MV up higher, makes me feel like the room is over-damped. Now I wonder if adding the six extra panels on the ceiling is going to have a negative affect. And I wonder if the room really needs diffusion and perhaps I was steered wrong.