First, thank you for the replies so far.
I was able to pick up a Model B with High Power fabric locally and with a return policy, just in case it doesn't work out for me. So far I'm not so sure I'm happy with it. That said, it is miles better than my old screen (an Optoma GrayWolf II by the way) so at least I've moved in the right direction.
The problem now is too much brightness, even with my AE-4000U set to Cinema 1 mode, Lamp Eco urned on, and with 700+ hours on the bulb already. If I get a new bulb, I'm pretty sure the image would be way too bright.
I knew 2.4 gain was more than I wanted, particularly for such a short throw distance of 125" and screen size of 106". However, I was hoping the narrow viewing cone, the retroreflective nature of the material, increasing the viewing area from 92" to 106", and the significant height difference between my eyes and projector would all help drop down the brightness from my viewing area to a more reasonable level and I'd get the benefit of no waviness. In practice, the brightness drop is noticeable from standing to sitting on the couch, but it's just not enough. Unfortunately, the projector is already as high as it can go on the wall shelves and I'm not about to sit on the floor.
The other negative side effect I'm getting is significantly more light spillage, causing black levels to now be a noticeable gray shade. This was of course partly inevitable going from an extremely dark gray 92" screen to a white 106" screen, particularly since my walls and low ceiling are also painted white (and not subject to change sadly). However, I've certainly overshot on the brightness mark so perhaps my setup would be better served by a lower gain screen material, which would solve both my abundance of brightness issue and lower black levels back down.
So at this point, I'm considering getting returning the High Power for another 106" Model B with High Contrast Matte White instead. I could also just get plain Matte White. Unfortunately, I've read here on the forums that the material will show waves and I might even have waves with a brand new screen. The only other option I've seen recommended here is to use a neutral density filter in front of the projector to reduce the brightness but I have a negative (though admittedly unexperienced) gut reaction to that approach.
Lastly, to quickly address a couple points made in the replies:
a) I would have gotten a Model C but there isn't room to mount it unfortunately
b) I also can't pull down the screen any further in my setup as it would go behind radiators and furniture. So there's no need to get any additional drop material on the top off the screen for this setup.