I was going to say the same as Steve. These GPS antenna spacing concerns seem largely folklore. It’s hard to imagine what is going to cause problems there anyhow, back-leakage of local oscillator from inside the GPS electronics back to the antenna??? In some cases I’ve seen confusion between gps antenna to gps antenna and gps antenna to say DME or VHF coms antennas and they may make more sense. Even if it exists as a real problem at all, many many gliders have flown sucesfully with multiple GPS antennas separated at most by a few inches. Including two of mine.