Yes, I agree that is the way they do it, but also after observing Craig's oven I came to several other conclusions. First, the material they use for insulating is not nearly as good as perlite (the oven was too hot to touch on Sunday), but it is much more dense, they use the insulating material AS the buttress along with the exterior layer of stucco which by my estimation is a good inch (thump test), and is not reinforced by wire (looking in the cracks of the stucco).
That is why I planned to use a belt of refractory concrete (non insulating). With the brick sailored, it will maintain the planned 4-1/2" of thermal mass, and will NOT rely on the insulation/stucco as a buttress.
How did you apply the perlcrete?