In my room, 14' x 20', when I had the speakers on the long wall, the soundstage is even with the speakers. With the speakers on the short wall, the soundstage varies depending on how close the speakers are to the back wall. In general, I think that the further away they are from the back wall, the more depth there is in the soundstage. Your theory seems to be true based on my experiences. Of course, you don't want the speakers too close to the back wall and you can get a general idea of where they should be by going to
http://www.cardas.com/insights/index.html
and clicking on "Room Setup." (In your room, Cardas would recommend that your speakers be about 8 feet from the rear wall.)
P.S. Rear Wall = wall behind the speakers
http://www.cardas.com/insights/index.html
and clicking on "Room Setup." (In your room, Cardas would recommend that your speakers be about 8 feet from the rear wall.)
P.S. Rear Wall = wall behind the speakers