Flat Earthers tend to bring up VHF and higher wave propagation as evidence the Earth is flat because these are line-of-sight. Ignoring for a moment that there's a limit to HF propagation (I can't talk to India at all, for instance), the instances of VHF propagation are rare and due to predictable phenomena like Tropospheric Ducting. You have tested this yourself I can almost guarantee as you've driven away from your favorite FM radio station and heard it fade and fade until it's gone after around 50 miles. AM stations go much further since they are low frequency HF. Using rare cases of VHF propagation as some sort of proof of flat earth is silly. Instead, predict when and explain why these events will occur on a flat plane.
The radio contact distance records for 109mhz or there abouts is likely the result of a rare tropospheric ducting.
https://proaudioeng.com/tropospheric-ducting/
These are records, not everyday contacts. In 99% of atmospheric conditions the 40mhz rule he states is absolutely true, ask any ham (like me)
The higher the frequency the more line of sight needed is the general rule
Interestingly 20m band and 40m band work at opposite times of the day because they are bounced by different layers of the ionosphere. One works only at day time and one only at night if i recall correctly.
The longest contacts are made by EME also called moon bounce, and this can be done even with high microwave frequency
"A new 10-GHz Earth-Moon-Earth (EME or moon bounce) world record has been set. On September 9, Rex Moncur, VK7MO, and Jim Malone, WA3LBI, completed a 18,949.4-kilometer contact using QRA64D. This extends by approximately 600 kilometers the previous world record of 18,337 kilometers held by DL7FJ and ZL1GSG, who used CW."
Here's a decent records page
https://www.ok2kkw.com/dxrecords.htm
EME and Tropo are noted on there, and that's what i talked about above. F2 is an ionosphere layer and in some frequencies that will go further than eme