Unless their documentation is out of date, which is possible, I don't think you can change the default values for Auto-channel on the 2.4GHz radios. Here is what I found:
Autochannel on 2.4 GHz only uses channels 1, 6 and 11. Administrators can remove only one of the three channels. If non-standard channels need to be used manual overrides can be done from the Overview page.
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