Old Smokey,
I thought I had this figured out. Now I'm confused. I hadn't thought of wave drag, nor had I thought much about EAS, etc. But of course compressibility effects can't be ignored. When I did the descent profile simulation on the microsoft sim, I started out at say FL400 at M.73 (maybe this is too slow). In the constant mach descent, the glide angle increased as you said. I understood this as an increasing CAS, and increasing glide angle. I didn't look at the transition regime carefully. But during the constant IAS descent, the glide angle seemed fairly constant. What you have said seems to fit what I observed, but I'll need to think a bit more on this.
Regards,
flybubba