Requisition Approval Setup Question

Hello,

I am in the process of setting up Distribution Lists for RSS. For most cases, I am using the Employee/Group Approval Authority. In doing this, I'm finding that I needing to have the same employee in 2 or more groups when the Requisition is routed to a different approver based on site. The system allows me to do this. The question I have is how does that work exactly. I can link the groups to separate mailing lists, but how does the approval process know which one to use?