ear level when seated assuming that your primary listening position will be seated. you want to tailor your 'sweet spot', where the sound is balanced and sounds best, to be at your primary listening position. this is easier said than done of course.

here is a little guide that will help you with horizontal placement. of course the ideal speaker placement doesn't work in every room.
http://forum.ecoustics.com/bbs/messa...79/129023.html