In the early years of FPV racing, we all thought that spacing the allocated frequencies equally across the available bandwidth is the best strategy to avoid interference.
But as many of us have experienced, such channel allocation does not often result in interference-free events, even when using "only" 4 channels at a time. By trial and error it became obvious that two channels on the upper band and two channels on the lower band yield better reception for everyone.
While playing around with 4 transmitters and a spectrum analyzer, I think I have discovered another piece to the puzzle: the frequency difference between the two signal pairs should be different!
E.g. CH1 and CH2 25Mhz are apart, and CH3 and CH4 15Mhz are apart. This seems less interference than when both pairs have a similar frequency differential.
I made this video to show the effects:
If you have knowledge, experience or opinion on this topic, please reply in the video comments, or in this forum thread!