Thanks to both of you! I tried making it deeper for the time being and it works much better. I'll make sure to get lump charcoal instead of briquets next time.
One question for you though Alan, with my current airflow, the air blasting from the side doesn't seem to go very far through the coals. I generally have to keep my steel very close to the hole the air is coming from, as the rest of the coals are cold. I probably need a stronger blower right?