So, Speakers set up on either side of a wide arch?

I am trying to figure out the best way to set up my gear in a new and rather odd room. It is "L" shaped open concept sort of thing. It is like a 21'x 14'room with a 10'x 12' room forming a sort of alcove area. One of its sides has an open staircase going along part of it. (8' ceilings) The long wall of the "L" is 24'. Just off center of the long wall is a 5 1/2' wide, 6 1/2' high opening to another room.

My first thought has been to set up my main rig so that the speakers are on the 12' wall that is at the end of the far side of the "alcove". There is a back wall and side walls there. But I have a second set of speakers set up just to either side of that 5 1/2' wide opening. They have back wall on the outer sides side but no back wall in between them, and are 5' and 9' away from any side walls, respectively.

The main speakers are the excellent Thiel CS 2.2s. The second set are Rega Camber 3.0 -- large and really sweet 2 way stand mounters. Both pairs are front ported. The rest of the gear is all in favor of the main set-up with the Thiels. But the thing is, I am not thrilled with how the Thiels sound on that 12' wall, and am impressed with how the Cambers are sounding. So maybe my intuition that the lack of a back wall would cause a thin, sucked out sound with a "hole" in my soundstage was wrong.

(Here I made an impressive diagram of the room, but the formatting gets lost when you preview or post.)

Anyway, and to the extent you can follow my description, is there any good reason not to set up the main rig with the Thiels so that they are on either side of this big empty doorway.

Thanks for any advice!