The inverted pyramid rebar stove is ubiquitous in Haiti. Lots of radiation and convection away from the pot. No air control. Pot is often placed directly on the charcoal which quenches the charcoal and interferes with good radiative heat transfer.
I cut up a scrap stainless steel kitchen sink, built a sheet metal outer box, put in 1" of ceramic fiber board insulation, and added legs and pot supports. The inverted pyramid grate will have the legs shortened and be placed inside the "sink". A slide gate with sets of progressively smaller holes will be added to the "drain" for air control.