One other thing. Those Mirages are omnidirectional, are they not? If so, perhaps they would like reflections. My M3-sis are bipolar, and the manual speaks of keeping side and rear walls clear of objects which would affect dispersion. That may factor into how your acoustic treatment goes.
I have too much stuff in my room and am pretty sure the soundstage depth is affected negatively, as both side and rear walls have stuff on them.
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