With me not having had a surround system for 15 years, I'll offer what a friend told me. I'll preface that his comment was specifically while talking about rear speakers.
To paraphrase him, he said it didn't matter. The movie makers, want your eyes focused on the MOVIE so all the important sound will come from the front. They don't want you turning your head around during a scene in the movie to chase a sound that went that way. Secondly, since you are getting ambiance and (his words) sounds of frogs and crickets out of the rears, it doesn't matter.
That said, a different friend of mine has a 7.2 all LaScala setup and it's outstanding.