ROS v7.14 upgrade of RB2011UiAS with five cAP ac access points, also on ROS v7.14. CAPsMAN configured as show below, i.e. frequency set to 5500, 5180. Most of the time, all five access points end up on 5180. My understanding is that 5500 (highest tx power) should be used unless CAC radar check fails. I really doubt this is the case because if I simply set frequency to 5500 alone, they power up fine on that frequency.

Later... changed the frequencies to 5500, 5660, 5580, 5260, 5180 and we've now got a spread: 1=5660, 2=5180, 3=5660, 4=5660, 5=5580 so maybe it doesn't like 5500 at this site - although if I specify just 5500, it's used. Does anyone know the logic about frequency selection? I've made lots of guesses but the algorithm from the designers would really help

Ask support.
They should know

Hmm... maybe. Support often aren't party to the inner workings/algorithms. But they should be able to ask.

I think old wireless driver performed a scan of all candidate frequencies and selected the frequency with the lowest number of other access points. New wifi driver might behave similar.

I have it the same way, and it works well for me, it only goes to the second frequency when it finds "a radar signal" once a month, it will be a mobile radar,