> I don't quite understand how the airplane shape made it easier to model the loading and positioning? (Not saying you're wrong, just doesn't fit my intuition and I'm curious).

You can approximate space shuttle reentry to roughly a 2d surface entering atmosphere. Because of airplane shape, the tile side faces atmosphere and the plasma goes around plane edges. Where as starship being cylinder doesn't have any separation boundary and plasma roughly goes more than 180% of the cylinder.

IR reflectivity of stainless must help a good deal for the unshielded parts. I wonder if the internal surface is painted or finished in a way to help radiate the heat away internally.

Is there any active cooling of any of the skin that we know of?

Ah, that makes sense!