Hi @pvanosta - I agree! The ML Masterpiece line is something special. I have a pair of Impression 11A's in a relatively small room, 11x20. Per ML's guidance, you want the rear woofer no closer to the rear wall than the diameter of the woofer. So in the case of the Expressions, that's 10". With ARC built in for the subwoofers and the ability to adjust their level +/-10 dB, you can eq for a lot of bass issues.
My bigger concern would be having the ESL panels too close to the front wall causing the timing of the back wave's reflection to be too early and smearing the front wave. You can address it with some absorption on the front wall, but these ESL's sound best when you can give them ample room to breathe. I have mine positioned so that the back of the ESL panel is about 50 inches away from the front wall. The farther away from the front wall you can get them, the bigger the soundstage will be. Hope that helps!