Custom Sierra 1 or 2 How deep does it have to be?

I have ordered Sierra Towers, and I am currently saving up for the Horizon: but I am planning ahead (way ahead-probably over a year before I can afford this) and I am wondering what is the minimum depth that a custom Sierra 1 or 2 could have.

The reason I ask is that my room is narrow and the couch goes from wall to wall (sort of) and I don't want the people on the ends of the couch with the side surround speaker right next to them. Currently I have some Dipole/Bipole speakers there which I don't prefer, but they were a way to have a speaker that did not stick out too far from the wall.

Would anyone else be interested in a design that minimizes the depth of the speaker?