Roaming (and band selection is a subset of roaming) is an almost entirely client-controlled feature. Ruckus supports "intelligent band steering" that attempts to direct 5GHz capable clients towards 5GHz, but if a client absolutely insists on 2.4GHz, the AP's will still allow them on, otherwise the clients will simply just stay disconnected.
The most bulletproof workaround for this is to create a separate 5GHz SSID and a combo 2.4+5GHz ID, so you can forcibly select the 5GHz one when you know the client is in a good spot for it.
Note that 5GHz has a much more difficult time penetrating walls and other solid objects compared to 2.4GHz, so if you're a bit too far from your access point, 2.4GHz may actually be the appropriate choice.
