Very nice write up. I am curious, is the long wavelength Responsible for the rise and fall in audio quality depending on where you are. I have had this happen as I was driving, the sound quality seemed to pulse.
Also I used to live right at the base of a tall mountain range there was a AM transmitter on the other side less than 100 miles away. During the daytime I could never receive it, at night it would bounce over the mountain and it was pretty clear.