FW rules, aliases too long?

[fai0]

Hi All,
I've setup and WAN load balancing. And I would like to divert the traffic by location as one of my Internet connection is faster for certain location.
I've added the IPs network to the aliases,but when i apply the aliases to the FW rules, an error show the aliases is too long. Is there any limitation of how many items per aliases? Or is there anyway to do that in a better way? Thanks~