Sux our old pics are gone, Hankster did a diffuser plate for a small diameter smoker that he claimed worked real well. As best I remember, it was a piece of sheet metal that was about 4" wider than it needed to be with holes cut near the edge at gradually closer intervals as you moved away from the firebox. The extra width was then folded over leaving half circle holes along the edges of the now correct width plate.
The folds gave it rigidity.
Tough to describe, but I tried. I also sent Hankster a PM, on the off chance he'd still have the pix.