So your rooms DON'T have four walls, a floor and a ceiling? I simply don't see how you can simply exclude these factors just to make your point. Yes, this is where we differ. My rooms are all fully enclosed because thats th only kind of "room" that I know of.

But if you do what you are saying outdoors where there are only three intersecting planes then I agree with what you are saying. The corner will add 9 dB to the free field response and it will direct the sound along the walls - so long as the source is within 1/4 wavelength of the corner.

But with the other walls present the situation is completely different.