Hi BNS , In this senario ,
In SEPM make 20 groups for each site and then assign one computer as the GUP.
The cleints will take the policy from the main SEPM , but the content updates locally from the GUP specified.
Symantec Endpoint Protection 11.0 Group Update Provider (GUP)
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007092720522748
Best practices for Group Update Provider (GUP)
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2008081810593048
GUP role can be assigned to any SEP client. When assigned the GUP role, a SEP client will act as a caching HTTP proxy - storing both delta and full revisions of SEP content. Other SEP clients can be configured to utilize the GUP for definition and content updates via LiveUpdate policiy from the Symantec Endpoint Protection Manager (SEPM).