Your prior statements are at conflict with that. You realize that satellites require LOS to operate right? That's why companies spend billions to keep them the globe in low or high earth orbit.
Radio transmissions go on forever, slowly degrading as the waves spread out.
If the Earth is flat, why don't the oceans fall off the side? Clearly not gravity, because that comes into play at roughly 300 miles in diameter, which is what causes mass to fold in on itself creating spherical objects.