Honestly, I wouldn't worry about that. Nobody sits perfectly still in a vise anyways for the duration of the movie. Sure, some people are a little more crazy, and they'll even cover their couch (leather seating) with less reflective things like a blanket or something when running the tones. If you want to be obsessive, go for it. Vicinity of your ears is good. Try it, and see if you like it. It doesn't take long to run the auto cal.