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To answer your question though, about UHF/VHF "falling off a cliff" at a certain point --

Let's just say it's INCONCLUSIVE. That fact doesn't lean Flat Earth, but it doesn't prove a globe either. It is inconclusive. What you bring up isn't braindead or stupid, or 10-times refuted as so many other NON-arguments (e.g., ships sailing over the horizon). Nevertheless, it is merely inconclusive and merits further study.

There is obviously something different about how VHF and higher radio signals propagate, vs. lower frequency signals. That is obvious. We don't know much about how the ETHER behaves after all, since they "did away with" the Ether years ago, even though it never stopped existing. We just know nothing about it now.

Knickebein bombing radar, on the other hand, conclusively falsifies the Globe model. There is no excuse or explanation. 

There is obviously something different about how VHF and higher radio signals propagate, vs. lower frequency signals.

Long story short, lower frequencies tend to "hug the earth", such that for optimal AM reception, you really need to have your receiver grounded, and elevation isn't really an issue.  VHF and UHF don't do this, they follow line of sight (pretty much so), and there is also "knife-edge" propagation, such that signals carom off of ridges and mountaintops (the "knife edges), and are reflected into valleys and such on the other side of the mountain.  There can also be multiple knife edges, such that the signal from the first knife edge ricochets onto the other knife edge and beyond, and theoretically this can continue for a great distance if your knife edges are lined up just so. 

There was a TV station in San Luis Obispo, California that could be received all the way to Nevada (at least in certain spots) due to the effect of the mountains that surrounded the San Joaquin Valley.  TV viewers in mountain valleys are heavily reliant upon knife-edge propagation, they certainly can't do LOS, simply because that mountain is in the way.  I grew up in an area that was kind of down in a bowl, and we didn't have LOS for anything except the local public TV transmitter.  Stations 20 miles away had to reach us via knife-edge off the hilltops that surrounded the valley.