Indeed, 1, 5, 9, 13 works really well. The slight interference caused by the minimal overlap is so small that it’s hugely offset by having four channels instead of only three. As I’ve said before, iirc, I think there is a potential problem in densely populated areas though and that is if anyone uses 1, 5, 9, 13 then everyone in earshot must use it otherwise for example channel 8 will interferes somewhat with a 1+6+11 user’s channels. So if you are going to do four-channel layout and have neighbours in earshot then everyone should get together and agree on this plan. Do you agree?