It seems to be the placement. I pushed them all the way back to the wall and the 'throatiness' went away, perhaps at the cost of soundstage. They are best about 30-36" into the room but I don't have the space for that. Need to put some casters on them, these babies are HEAVY!
I assume the best left/right orientation for the horns is on the inside, away from the walls, is this correct?