Over the years this subject has come up time and time again. What makes the best diffuser for the mini? Terra-cotta Saucer? Cast Iron Frying Pan with the handle cut off? Steel plate? The Steam Tray that came with your pot?
I use nothing more than a disposable aluminum pie plate with a few cups of water in it. Inexpensive and they work great. Best of all, after the smoke I just toss them in the trash. One less thing to clean!