If you go into studying Raleigh scattering assuming the earth is flat, instead of round, the math resolves just as cleanly to support a flat earth.
I think the above quote is a bogus claim.
How does the "math resolve ... to support a flat earth?"
How does 'Rayleigh scattering' even depend upon 'Earth shape assumptions'? The two are independent phenomena.
If you have 'Raleigh-scattering-math' that supports FET,
please present that math.The OP does not seem to be a question of "resolving the math"
(whatever that means), but a question of logic:
If the sun never sets (FE model), then why is the sky not everywhere blue all the time? If the sun is a "spotlight" illuminating only one portion of the flat disc at a time, then the Raleigh scattering at right angles to that intense light beam would illuminate the entire disc's sky with [predominantly] blue light all the time (even over areas that are not being directly illuminated by the "spotlight" at that moment). Because of a bright sky, there can be no nighttime darkness anywhere. That is not what we observe. We daily observe the absence of light in the sky (which we call nighttime). The globe model explains this well.