Why does drag coefficient decrease with Mach number in the supersonic regime?

I’m trying to understand why the drag coefficient decreases in the supersonic regime with Mach number. While it is easy show this using supersonic, potential flow theory, I’m looking for a more physical explanation.

My initial thought is, as freestream Mach number increases, the shocks should become stronger (even though they are more oblique, the normal component to the shock is still larger). Where is this train of thought going wrong?