You are mixing RF Manager and RF Management Policy.
The RF Management Policy in a site in XCC is exposing the following parameters for the configuration of the APs like SSID, MTU, VLAN, 802.1X credentials, etc
The Radio Profile is more for channel, power and interferences
You can re-use an RF Management Policy between several sites if you have the same SSID there.
I use this a lot to keep the things simple.
Modifying one object can adapt the config on multiple sites.
There is a high added value to go for site structure.
Please check here https://www.extremenetworks.com/support/documentation/extreme-campus-controller-latest-documentation/ for the deployment guide.
FYI we manage here with a couple of XCC 27 sites with 2100+ APs. The version is 5.36