NTP client not polling from nearest DC

Hi- I have multiple sites globally with Domain Controllers configured as
reliable time servers for their respective sites.
The issue is that my XP clients aren't talking to the nearest reliable time
server. Even after I set my local site's DC again as a reliable time server,
my clients still look to a DC from a distant site. (e.g. New York clients
talk to a Sydney DC). Hoping someone has come across this before and has a
fix. Any help would be appreciated. Thx.