How much of an air gap is needed at the back of the grill opposite the vent on a 22.5 inch LBE? Is 3.5 inches enough (i.e., the height of the circular segment)? That would let me have a 19 inch diameter stone where I could land (in theory anyway) an 18 inch pizza. If that's not enough of a gap, I won't sweat it. A 17 inch pie would be fine too. Actually, most of the time I'll probably be making 12 inch pies, but since I'm building a 22.5 inch LBE, I might as well make it capable of handling a true NY sized pie.

In a circle of 22 inches diameter, the area of the circular segment cut off by a secant with a height of 3.5 inches is 38.9, which is about 10% of the total area of the circle. So the gap at the back of the grill would equal 10% of the total area, while the stone would occupy 90%. Will that be sufficient airflow?