i'm changing my 5.1 system to 7.1. My rear speakers will be flush mounted on the walls behind the couch (about 15' behind) and pointed straight ahead. How high should the speakers be mounted? my side surrounds are dipoles and mounted about 2 feet above ear level. Would 1-2 feet higher than ear level be ok for the rear surrounds? I'm mounting these today and was wondering if anyone could let me know.