Explicit GUP List - is it possible to assign /16 subnet, not /24

We run SEP12.1.5 in our environment and are in the process of configuring explicit GUP Live Update policy. The issue we ran into is that we cannot assign /16 subnet to a specific GUP.

For example an explicit GUP entry will look like 10.1.100.0 and client's IP Address is in 10.1.100.0/24 subnet then it will get the updates from the GUP, but if the client's IP Address is in 10.1.101.0/24 instead it will not. Making GUP entry 10.1.0.0 does not work. Is there a way to make the system treat the entry as 10.1.0.0/16? What are the other ways of effectively accounting for roaming clietns?

Thank you