Challenging Room Node

I have a dedicated listening room that I have treated with GIK panels in the corners, first reflection points and behind the speakers.   I have had my 800 D3's in a number of positions and thought I had them locked in.  I ran some frequency sweeps using some test disks.  There is a node at 60hz so bad that the narrow frequency almost disappears.  When I stood up to move about the room it came back with a roar as soon as my head got above 4 1/2.  I was always thinking in 2 dimensions but evidently my room (17.25 x 23.13 x 8.54) has some vertical issues.  

I have mitigated pretty well by moving the speakers closer to the read wall but i give up some clarity.  I also think the speakers sound more dynamic when I stand.  Anyone encounter this issue and mitigated it?