You can schedule 'gross surface area' also 'gross surface area of the bottom of the slab'. I have also had success creating an additional 1mm material composite on the bottom/top that overrides all other material priorities. It's a pain, but it cannot be seen.
I agree that there should be a 'top surface area to perimeter edge' option Back in the day 'Area' would work just fine.
Maybe someone has a better idea.
Versions 10 to 27
Metabox Prime-X P775DM2-G (Clevo),
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