I’m not sure I understand well what you want, but maybe the end of this can help you.
I don’t really understand the iOS code but what I know is that various beacons set with the same UUID can create a larger region.
Nearable monitoring primarily uses the Nearable packet, with iBeacon packet only used as support. So even though technically each call to startMonitoringForIdentifier will take up one region, enter events should still trigger even if you exceed the 20-region limit.