What nags me is whether or not this is the way to solve the problem. I got this idea from owning a Rel sub where they suggest in hooking up the sub out of phase which may reduce bass boom.
Of course it is not correct - you are changing the impulse response significantly. This may be why it sounds more spacious...probably more laid back - less distinct on transients or muddy. The inteference pattern that you create will have a null down the center line of the room (if it is symmetric). A better solution would be tone control or PARC or placement further out into the room. Electrostatics are designed to be placed well out in to a room (less bass reinforcement) and therefore it seems likely that ML's will bass heavy if placed up against a wall.