It seems like a room interaction to me also. These speakers need room to breath based on my limited time with a couple different Rockport speakers, and plenty of current delivery to properly drive them. Get them right though, and you will have speakers to rival all others at any price. They are truly magical when all things are correct.
Pull them out into the room a few inches at a time and see what happens.
Pull them out into the room a few inches at a time and see what happens.