Acoustic panels on ceiling

Directly above the listening zone.  Ideally this would be a first reflection point and would help towards overall creation of a reflection free zone when used with absorption/diffusion in front, sides, and back as well.

Yeah... I have all that, absorption on side wall, absorption and diffusers in front and back wall. Just ceiling missing.

You are saying right above where I sit? Maybe toward the front a bit? Mirror trick does not appear to work for me for ceiling 

I've been in a few concert halls where the panels are "floating" in mid-air. They are suspended by wires. You might try putting on an angle. If I were going to do this (panels on ceiling), I'd put them in the center of the room. YMMV.

In this situation I would contact GIK directly and e-mail them pictures of your room as it is currently  set up. They are very helpful in helping their customers utilize their products.
David Pritchard