I haven't tried the charcoal in a ring. I just place a big split of hickory and the rest of the space with lump. I leave a small space in one corner that joins up to both the wood and lump. After preheating the chamber and starting a small amount of lump in a chimney, I add the well started lump to the empty corner and close it up.
I open the in and out vents wide open to establish a good flow through the reverse flow in the safe. Then I adjust the vents to my pre established settings for the temp that I want. Then wait..........
PitMaker Combo - Safe & 30" Grill Meister