You don't necessarily have to entirely cover a boundary surface, although the floor and angled part of the ceiling probably should be. The other surfaces may have partial covering. If you toe-in your speakers like I do, I'd want the adjacent sides absorbent, which would be beside and behind the speakers. That just helps reduce early reflections, something the directional nature of the speakers already does but the absorbent room treatments go further in the right direction. The reflection from opposing walls tends to give an impression of spaciousness so I wouldn't want those walls to be overly deadened. Experiment to find what sounds best.

Would you be opposed to using this stuff?

• Sound Absorbent Foam (wedges, pyramids and corners)