Games : Why Can't My Relay Antanna Control My Drone

I have a drone with a radio antanna broadcasting in a 20km radius. When it is near Base A (5km broadcast radius), I can control it. Base B is 4km from Base A and has a broadcast radius of 50km. My drone can successfully travel to Base B.

I would expect that if my drone is within 100m of Base B, I would be able to lower its broadcast radius to ~300m and still have a two way channel, using Base B as a relay; however when I lower the drone's broadcast radius below the distance to Base A, I can no longer control its gyro and thrusters from Base A. Surprisingly, I can still see the camera. Why is this?