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I'd say it's the same reason we can't see the Eiffel tower from the East Coast, not even with a telescope.

Human eyes, vision, and radio waves aren't infinite. The very air has SOME moisture in it, not to mention pollen, pollution and other particles, which is going to affect the perfect lossless propagation of radio waves.

There is definitely an *ether* component to radio wave propagation. They (mainstream science) only "got rid of" the Ether (or Aether) out of necessity, to defend the moving earth and/or globe paradigm. That's it! So yeah -- ether is almost certainly a real thing. Radio waves propagate through the ether.

Considering science doesn't "believe in" the ether anymore, I'm sure they wouldn't ascribe anything to it either. Such as: changes in propagation (during the day, on a yearly cycle, on the sun's cycle, etc.) But I bet all the "variances" in propagation are due to changes in the ether. Definitely something that real scientists should pursue.

But would the signal just drop off entirely, like falling off a cliff, after about 100 miles?

The Longley-Rice maps (which are based upon GE, of course) seem to indicate that.  Seems to me that in an FE scenario, yes, ether would have its way with the signals, but the signal would fade out gradually to zero, even over a totally unobstructed surface such as open water (which is why I used the LR map for a station that is on the coast and is omnidirectional), rather than just being there, and BOOM!, it's no longer there.   In a GE scenario, it certainly would be a case of "BOOM! --- it's no longer there".

If you study such maps over a varied terrain, such as mountains or a dissected plateau (as in southern Appalachia), you'll see that there are certain ridge tops and so on that are "sweet spots" for reception, and this, too, can be verified by going to these locations and putting up an antenna.  I am on kind of a ridge and there are TV stations about 85 miles from me which, according to the LR maps for these stations, land smack-dab on my property, while totally missing lower elevations a short distance away, and sure enough, those are the exact stations that I get.  The signal is weak, it takes a top-flight antenna such as the Televes DATBOSS (which is what I have) to pick it up, someone with rabbit ears wouldn't stand a chance getting it.  UHF parabolic dishes yield even more satisfying results.

So now "refraction" bends radio waves too? 

Oh, you have to read their explanation for how those UHF waves went for many miles ... where they made up this idea of "tropospheric ducting" just to explain that one.