Old Smokey,
I follow what you are saying about the drag change, but I try to understand this in terms of L/D. The glide angle is proportional to L/D. The drag may be changing but is not the lift also changing so as to have constant L/D? I'm only talking about the case of a constant IAS descent here (I agree about the initial constant mach descent having a changing glide angle). TAS may be changing thru all this, but I think that what really matters is L/D.
Any thoughts?