CAS server will automatically aggregate client IPs either into CIDR blocks or ASN (bigger bucket).
That depends on your CAS configuration. The default mask for these locations is not 20 (unless you changed the default). Default mask equals to 'Original CIDR' = as defined for a CIDR block in bgp table (to view the raw table see \config\bgp.zip file on CAS). You can change the default aggregation mask in Tools->Admin Console->Advanced Properties Editor->PCS_AGGREGATE_MASK1 property (type mask in search field to easily locate the setting)