I agree, with room acoustics the proof is in the pudding. It often takes trial and error to get the response that sounds best to you. Any experimentation will put you well ahead of most, who simply put it in the one place they decided upon and left it there.
I wouldn't throw out all theory, as there is nothing more practical than good theory.
Sometimes, a few "rules of thumb" can save some time, although I'm sorry it didn't help in your case.