When do I get notified when monitoring an iBeacon region based on UUID?

I want to build that gets notified (even when in the background) when it gets in range of any iBeacon with a given UUID.


I know I could monitor an individual region for each of my beacons, but if I understand correctly, on iOS, I am limited to 20 monitored regions.


So the other alternative is to monitor a region based solely on its UUID, but then when do I get enter/exit notifications for that region? Whenever I get in range or out of range of any beacon with the same UUID, or only when I get in range of the first one and out of range of the last one?