The flat guys believe that there are no geostationary satellites. Instead, they think signals from these are broadcast from hovering aircraft at high altitude. There is a simple way to disprove this.
While this is an interesting thought experiment, it is based on a couple of assumptions.
Consider two houses with satellite TV dishes a couple of hundred miles apart. Both have to point directly at the object broadcasting the signal.
Actually, this is not completely accurate. RET teaches that signals bend or refract in the ionosphere. As such, neither dish is pointing directly at the object. Instead, each dish is adjusted to receive the best signal. Therefore, neither dish is a reliable indicator of the true source.
If the signal comes from a satellite, the angles of the two dishes would be very similar. If the signal comes from a balloon or other much lower altitude object, the angles of the dishes would be greatly different to each other.
This is the other assumption. ("a satellite" or "a balloon") While both receivers may perceive a single source, the existence of more than one source has yet to be disproved or is at least still subject to debate.
All that said, I do like the proposal. It just seems to assume too much.
Regards.