SmartRoam is applied per WLAN on all APs that advertise/service that WLAN.
It can be used only on your WLAN with Apple clients for example.
Not configurable from the WebUI, the Standalone AP or ZD CLI configuration mode commands are provided in KBA-2277.https://support.ruckuswireless.com/answers/000002277
You can 'set roam_factor wlanX 3' for typical application benefits, up to a factor value of 5, but is not recommended higher,
although it can be set as high as a 10.