What it does when mounted on a wall is make that wall vanish with regards to first reflections so it does enlarge the room in a sense. You won't get any comb filtering due to reflections from the wall because with the transducer at the wall the direct and the reflected wave are always perfectly in phase. This gives a 6 dB increase in sensitivity as well.
BTW, flush mounting with the wall gives cleaner HF performance than the mystical cantilevered mounting facing the wall with a gap. All that does is diffract HF from the cantilever and provide multi-pathing to the capsule opening from all around it.
Bob
P.S. Glad to be back now that the constant, information free distraction is gone.