I would guess that this is due to the jamming antenna's visibility over the horizon. You can't jam a signal in the air, all you can do is transmit a jamming si

I would guess that this is due to the jamming antenna's visibility over the horizon. You can't jam a signal in the air, all you can do is transmit a jamming signal towards where the receiver should be. And if the receiver is on the ground, out of your line of sight, then you can't do anything about it.