This is a small, 15 oz, can that held black beans.  The bottom was removed with over-lapping
 "church key" cuts - as can be seen in the shadows.  It turns out that this can loves max up draft
primary air.  But not all burn pots do.  Some perform worse when they are on this test platform.
I suspect it has to do with the strength of the up draft and/or its turbulence.

It turns out that the 'quality' and 'quantity' of both primary and secondary air, as well as the draft, 
are important variables in the TLUD system and must be carefully balanced for best performance.