I've been following this war very closely, and it appears they are able to send drones HUNDREDS of kilometers to hit targets deep inside either country.

Way beyond what should be possible if the earth were a sphere.

The frequencies used in drones are VHF and higher; certainly the wrong range of frequencies to be "bouncing off the ionosphere" or hoping for a lucky day with some "tropo ducting" or similar.
HF (high frequency, or 3 to 30 MHz) is the radio frequency range that bounces off the ionosphere (or the Firmament, depending on your cosmology).

Here's the thing -- any day of the week, you can get much further with a YAGI antenna on VHF and higher. But how? It doesn't bounce EVER. All a Yagi antenna does is FOCUS the radio transmission (and reception) in a single direction. Like a funnel for the RF energy.
But a million times zero is still zero. How can you amplify a signal that unfortunately went out into space and was lost? You can't recover something that was completely lost.

So however the Russians and Ukrainians are doing it -- on a daily basis -- it isn't something that should work on a globe earth.

I will say this: the antennas they are using are certainly small, which suggests VHF and higher. I don't see dipoles and vertical antennas with a bunch of radials getting bombed in the daily drone footage that comes out. For the non-hams, HF antennas are always quite noticeable, and take quite a bit of real estate. We're talking dozens of feet of wire. It has to do with the wavelength of the frequency being used.

Not to mention the bandwidth would be too low on HF. The higher the frequency, the more data you can transmit in a second.

TL;DR - you don't need to go back to WW2 (nαzι radar, bombing of Britain using VHF beams to guide the bomber aircraft) when we have current-day examples of military VHF usage proving a flat earth!