My guess, upon seeing your subject line, is that these computers are turned off for he weekend and you are only storing 3 revisions in the SEPM. When these machines come online on Monday morning and try to request definitions, the SEPM does not have enough older revisions to build the delta package, so instead it sends the much larger full definitions file.
If this is the case, increase the number of revisions from 3 (1 day's worth with default settings) to something closer to 9 or 12.
Admin > Servers > Local Site > Edit Site Properties > Live Update > Disk Space Management for Downloads. Up the number.
Title: 'Best Practices for configuring the number of content revisions to keep in Symantec Endpoint Protection Manager'
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2009020514050748
(If I understand correctly: you want your clients to run LiveUpdate instead of getting updates from the SEPM?)
sandra