Today I fired the man in the moon doll head. The approx thickness at the mid/thickest point is just over an inch.
It fired slightly longer than a much thinner piece of clay, but not significantly. When removed, I checked and it had cold spots. (Or spots not as red as others) I let the piece cool gradually to avoid shocking the clay.
When completely cooled I turned it over and noted that the bottom of it was almost raw clay and had micro cracks in it. Thinner than hairline and almost unnoticable. The microkiln does have its limitations.
I believe that if the piece had of been upright (instead of laying on one side it would have heated more evenly and probably would not have had the cracks.
On a second firing, the cracks become more noticeable.
UPDATE: I just found out that fixing little non structural cracks is extremely easy. The solution is to fire some of the same clay along side of it as dust, and then you can mix an epoxy with the ceramic dust and essentially spackle the cracks