Hi Jim, I may still be getting this wrong but where is all the insulation around the fire box?
I am no expert having only built two stoves myself but I am sure the insulation is a critical factor!
It seems lots of folk are now incorporating ceramic fibre board, I used a vermiculite mix on my first build to encase the whole fire box and burn chamber.
I know your proposed design is different from mine but perhaps a picture might explain better than words.
I also recommend a blanket riser as they are so quick and easy to build.
Have you looked at Thomas’s 8” build and use of ceramic fibre board?