looking for some ideas

[jon in mass]

well the area of the 11 inch opening is 92.93 inches and the area of the cercumfrance of the 11 inch opening and a plate 3 inches up is also 92.93 inches so i hopefully wont need to tune that fish. i am wondering about how close do i make the two plates

[Gizmo]

This is difficult without a drawing or pic...
Do you mean the gap between 2 plates as in Firebox roof and baffle plate? Cause an inch spacing would work to step down the heat - as long as it can breathe ....