Rob,
Its a count of the number of routed hosts, taken from the encap file and the BGP announce list.
Small math bug, but the number of hosts was right. So about 10% of the 44/8 allocation actually goes somewhere.
10/22/16 Routeable Ampr.org 44/8 Net Stats: ENCAP Total Hosts: 1224922 ENCAP Percent: 7 BGP Total Hosts: 581204 BGP Percent: 3