Ceiling diffusion

You will have to experiment. I've done all 4 variations with sucess. Depends on room or your taste. Not an exact science.

Armstrong, yes the ceiling tile people, makes a 'wave' product that is adaptable to home use. Check it out at their web site.

Most likely the first reflection point but experiment.

Diffusion directly overhead works the best to get the most impact from the panels.

You can try diffusion or absorption at the first reflection points. I have diffusion at the first reflection points on my ceiling, but I want to try absorption to see how it sounds. I also have diffusion directly overhead.

Let me know what you find. It's going to be some time before I experiment.