Is my room 11 x 14, or 11 x 20?

Here's the story: My listening room, measured from wall to wall, is 11 x 20. However, the wall on which I've got the speakers, which is the only possible placement, runs some 14 feet from one of the side walls and then opens up into another room. This six-foot opening does not close, doesn't have a door, etc. Consequently, the portion of the room I'm actually using is roughly 11 x 14, though there is no wall on one side for another six feet or so. My chair, of course, is positioned accordingly. (Hope that makes sense.)
When I'm reading about speakers that are supposed to be good in rooms of one size but not another, should I think of the room as being 11 x 14, or 11 x 20?
Thanks.
-- Howard