It's not a "spherical cow" assumption. It's a scaling issue. Deposing radiation over the a membrane (the surface of the skin) is different to depositing it thro

It's not a "spherical cow" assumption. It's a scaling issue. Deposing radiation over the a membrane (the surface of the skin) is different to depositing it throughout a solid body. Please don't say "spherical cow", as it's a bad analogy.