So I've been wondering about the up firing and reflections and angles, but more theoretically than practically since I am convinced to try down firing first.
The sound comes off the speakers in a diffusion pattern that's more cone like than line like, and it gets further diffused (and reduced in strength as it does) hitting the ceiling. Some part of the sound leaves the speakers at a wide angle and goes straight to the listener. If you need an angle that is is more horizontal (say 60 degrees from horizontal rather than 45 or so you have drawn), a lot of that direct sound hits the listener and less of the reflected. For more "up" angle (say 25 degrees from horizontal) for a close-up seating position, this is minimized, the further the seating position the worse the angle gets.
Are these speakers more directional than most, and so this is not really a factor?
Or is there a sweet spot not just to get the angles right, but to also not be too far away (and so need a sufficiently aligned angle you get too much direct sound)? Too far and the speaker has to angle down toward you too much and you hear it, rather than the reflection?
So if one does this, do you actually use straight lines and equal angle reflections, or is some power diffusion calculation needed to ensure the reflected sound is substantially greater than the direct?
(But that even more supports that people may fail at this by getting the angles wrong).