I am not sure if I understand your geometry. Are you trying to make a horn, a TQWT, or a TL? It sounds like a TQWT with the small end at the start of the taper, then 4 feet of straight line tapered, a fold into something else, then I am lost. If you could expand you description a little maybe I would have some constructive comments.

I am also using a smaller room (14 feet x 14 feet w/ 8 foot ceiling) for my stereo system so I have a bit of experience. I have several medium to big floor standing speakers residing in this space with pretty good results.

Martin