The ground plane in your RC systems is composed of the wiring in your system, primarily the ground wires on the servos and battery and are acutally the other half of your antenna, that long single wire attached to the input coils on the receiver is only half your antenna system. Any other metal(s) in the area might act as deflectors, directors and or shields but are not of general significance unless they exceed the wavelengths of the signals of interest. There are many basic studies of field strengths and how they are modified or utilized if you search the literature along with capture area and noise generation.