I followed the Pit calculations.
The opening into the fire box is actualy slightly larger than needed.
I agree its radiant heat but felt I was getting a good draft.
The stack is 2" higher than the pit calculations suggest.
The stack however only rest 2" inside the chamber, it does not go to grate level.
here is a blog to the build.
and here are my calculations.
thanks for taking the time to help and sorry about hijacking the thread