Sorry, I don't intend to be mean or rude here, but those are not theories.
Seriously? Well here we go with dictionary links.
https://dictionary.cambridge.org/us/dictionary/english/theory"something suggested as a reasonable explanation for facts, a condition, or an event"
The facts are that one frequency travels further than the other. I suggest (as a reasonable explanation) that one frequency travels better through air and therefore travels longer.
https://www.collinsdictionary.com/us/dictionary/english/theory"A theory is a formal idea or set of ideas that is intended to explain something."
I suggest, as an explanation for why one frequency travels farther than another: One frequency travels better through air and therefore travels longer.
http://www.businessdictionary.com/definition/theory.html"A set of assumptions, propositions, or accepted facts that attempts to provide a plausible or rational explanation of cause-and-effect (causal) relationships among a group of observed phenomenon."
The observed phenomenon is that one radio frequency travels further than another. The assumption which attempts to provide a plausible explanation for the observed phenomenon is One frequency travels better through air and therefore travels longer.
They are not even hypothesis.
Seriously? Well here we go with dictionary links.
https://www.merriam-webster.com/dictionary/hypothesis"a tentative assumption made in order to draw out and test its logical or empirical consequences"
The tentative assumption made in order to draw out and test its logical consequences is: one radio frequency travels better in the air therefore travels further
https://www.vocabulary.com/dictionary/hypothesis"a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena"
A concept that is not yet verified but if true would explain why one radio frequency travels further than the other is: one radio frequency travels better in the air therefore travels further
"a proposal intended to explain certain facts or observations"
A proposal intended to explain the observation/fact that one radio frequency travels further than the other is: one radio frequency travels better in the air therefore travels further
https://www.dictionary.com/browse/hypothesis"a proposition, or set of propositions, set forth as an explanation for the occurrence of some specified group of phenomena"
A proposition set forth as an explanation for the phenomena of one radio frequency traveling further than another is: one radio frequency travels better in the air therefore travels further
https://www.livescience.com/21490-what-is-a-scientific-hypothesis-definition-of-hypothesis.html"A hypothesis is a suggested solution for an unexplained occurrence"
The unexplained occurrence in the flat earth model is that one radio frequency travels further than another. A suggested solution to this occurrence is: one radio frequency travels better in the air therefore travels further
They are merely unsubstantiated statements.
A perfect example of an unsubstantiated statement as shown by the evidence above (and below).
Now i'll send you some more links
https://radiojove.gsfc.nasa.gov/education/educ/radio/tran-rec/exerc/iono.htm"Earth's atmosphere, however, acts an opaque barrier to much of the electromagnetic spectrum. The atmosphere absorbs most of the wavelengths shorter than ultraviolet, most of the wavelengths between infrared and microwaves, and most of the longest radio waves."
https://www.electronics-notes.com/articles/antennas-propagation/propagation-overview/atmosphere-atmospheric-effects-on-radio-propagation.php"The various effects like reflection, refraction, diffraction, etc all come together in a real way as radio signals propagate through the atmosphere. The signals are affected by a variety of factors enabling signals to be detected near and far dependent upon a variety of factors."
https://calhoun.nps.edu/handle/10945/5353https://ieeexplore.ieee.org/document/5261619