The ceiling has a 2" Vicoustic absorber above the speaker and two GIK Gridfusors per speaker.
I am procrastinating ceiling trials. One, because it will be a pain in the butt. Two, because until I can mount a panel properly up there, anything I put above my head must be able to fall off the ceiling and not kill me.
I know from my trials on the sidewalls that a pure 2" absorber and the EPS (polystyrene) Gridfusors are not optimal, for me. I have found that at first reflection points I prefer a mix of absorption and scattering/ reflection. On top of that, I prefer maple and walnut as materials to build the panels. My favorite panels are the Stillpoints Apertures. I have used that design as inspiration for my panels, but I changes some things around. Among the changes, each position has an increase or decrease in absorption/ reflection. I also use maple to build them.
So someday, I plan to build the right solution for the ceiling. If you aren't willing to build your own, the GIK alpha traps are pretty good for the money.