How does Aruba Clearpass calculate concurrent endpoints?

They say the following in the documentation

" If we believe that ALL the endpoints will be concurrently connected to the network, we will need to license for 9,000. However, given the network data available (e.g. DHCP max pool size and lease times, max firewall session usage, etc), we are able to determine that only 6,000 endpoints are ever concurrently connected to the network and therefore we only need 6,000 Access licenses. "

But does anyone have any information on the accuracy of doing this with DHCP? Also does this require integration with IPAM/DHCP server or do they snoop something in the network?