@Underworld's reference got me wondering about this, so I dug into it. There's nothing I could find in LuCI to set channels, so I just manually edited the config (RT3200, but should be same on WAX202, I'd think).
$ cat /etc/config/wireless
...
config wifi-device 'radio1'
option type 'mac80211'
option phy 'wl1'
option band '5g'
option htmode 'HE80'
option cell_density '0'
option country 'US'
option channel 'auto'
option channels '1-100' <-- added this line
option txpower '6'
option disabled '0'
$ service wpad restart
... get disconnected, wait 2-minutes or so for DFS to do its thing, and reconnect ...
$ grep chan /tmp/run/hostapd-wl1.conf
channel=acs_survey
chanlist=1-100
chan_util_avg_period=600
$ iwinfo wl1-ap0 info | grep -i chan
Mode: Master Channel: 52 (5.260 GHz) HT Mode: HE80
Center Channel 1: 58 2: unknown
So, it looks like it worked, or at least hostapd didn't barf when it saw the channels spec.
Refs:
https://openwrt.org/docs/guide-user/network/wifi/basic#common_options
https://github.com/openwrt/luci/blob/master/modules/luci-mod-network/htdocs/luci-static/resources/view/network/wireless.js