First, nice looking pit! Excuse me for barging in, just trying to learn a little. I'm assuming there are no air intakes other than that coming in through the cooking grate? Makes sense when you look at the built in pits, most don't have any air intake.
Question for those experienced in the cooking style: is this common and would adding intakes help any?
PS:landarc's suggestion for a raised fire grate should make for a cleaner fire, regardless of how air gets to the fire/coal bed.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.