I think the GreyWolf is retro-reflective like the Da-Lite High Power. Can anyone confirm ?
If it is retro-reflective, then the issue is that if the projector is mounted too high and too close (ie it fires down at a steep angle) then a seated viewer will be outside the viewing cone but will see a bright image when they stand up. If the projector is table mounted, OR hangs down fairly low, OR is quite far back, then the angle is not so steep and a seated viewer should be OK.
I am surprised that screen mfgs don't talk about this more.
My 4x8 sheet of Matte White Formica has no such problems