Cross domain tracking between subdomains

Hello,

We've got link tracking setup using the c6-c9 variables which works fine for links on the same subdomain, but link tracking with those variables fails for links that take the user to a different sub-domain. I've gone through various previous posts on cross domain link tracking but I'm not sure their configurations are similar to ours and if there's something simple that we're missing.

It's difficult to understand what I need to start looking at, and/or what specific information I need to provide to get support -- please advise.

Thanks.

-Sid