I suspect that it is the thin profile of the on-walls.

I was impressed by the sound of my M2s (center channel) when I tried them as mains. Being a small bookshelf, they were obviously lacking in bass, but the mids and trebble were every bit as much a delight as the M80.

Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!