That's thermal conductivity, not penetration. About the only thing that can be reasonably uniformly heated in a microwave at continuous full power is a water-b

That's thermal conductivity, not penetration. About the only thing that can be reasonably uniformly heated in a microwave at continuous full power is a water-based liquid and that only because of convection. Put a slab of meat in for a minute at 100% power and it'll be still cold in the center.