Can't speak for others, but our particular products come in singles, pairs, and 3's depending on the product. 242 wall reflection panels and front wall panels come in 3's. Tri Traps, and 244's come in pairs. Monsters come singly. Purely a matter of maximizing the space in a shipping box for minimal cost.
The thing I'd be concerned about in that room is getting enough broadband bass control since you can't use the front corners. I'd also very strongly recommend lining the cavities where the speakers reside with at least 2" thick absorption all around to keep cavity resonances down to a minimum.
Bryan