I think speaker positioning may be a more significant factor here. I'm guessing the room is rectangular, rather than square, so you are likely to have different reflections and different standing waves when 'firing' sounds from these different positions.
Have you tried swapping over the speakers, to see how they perform in each others places?
I also wonder whether the HS7s are too close to the wall, given they are rear-ported. They look to be almost touching the wall, which would likely contribute to the uneven bass response. Something like a foot away from the wall should help...