Sparky - 3 things going on, same as any wood/charcoal grill.
#1 radiant heat transfer is off of the coals. (just like your charcoal grill)
#2 convection heat transfer is from some hot air - not really manageable due to open style
#3 smoke carried by hot air - not really manageable due to open style
Charcoal grills are essentially infrared cookers (shocking I know - think on it for a while) but the heat is uneven (due to charcoal coals distribution and burn rates) and the tunneling effect when coals are too close one another and create hot spots that are both infrared and intensified convection...