I'm just getting started building forms for foundation slab for 42" Pompeii. On page 13 plans call for 73" x 86" foundation and a 65" x 78" block stand but on page 66 plans are for 80" x 94" foundation and a 72" x 84" block stand. 42" interior diameter plus 4.5" of brick on both sides of dome = 51" plus 3" of insulation on both sides = 57" leaves 8" for framing/finishing. Right??? why larger stand?

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