RE: True range of RC signal
Three miles is around 15,840 ft. For the most people, maximum visual range is less than 1000 ft. I have seen Curtis Youngblood auto from 2000 ft, so let's use that number.
If you fly a model as close as you can to the other field, it will be 12,000 ft. from that field and 2000 ft. from you. Signal strength reduces with the square of distance, so any interfering signals from the other field will be (2000/12,000)^2 = 0.027 of your signal. Thats a difference of -15 dB. Interference would have to be about 10 times stronger before your receiver would notice.
If you restrict yourself to no more than 1000 ft. in the direction of the other field, then the difference is -18 dB. That 3 dB extra means the interfering signals will be relatively half as strong as they were when you were 2000 ft. away.
You would have to be flying about a mile away in the direction of the other site before you noticed any effect. At that point you would mostly be in control, but will get hits or holds (depending on whether you're using PPM or PCM). If that happens, just turn back towards yourself.