Sailor course. Got it. I know I've read that before, but it didn't stick.
It's the mass of the wall and insulation that creates friction with the floor, which, in turn produces opposition to the lateral thrust. It's an oversimplification, but, since vermiculite and perlite are basically massless, the insulation is providing the equivalent mass of about 1 more inch- for a total of about 5.5" of masonry.
With an oven with this dome construction, dome height and interior diameter, in your opinion, theoretically speaking, what's the minimum width of masonry that would counteract the lateral forces?