This is correct. And certain bases see certain places more often. In EWR we see Canada more often than IAH, and they see Mexico more often than us. Here's an example of a trip I have next month that touches multiple bases:

Day 1: EWR-STL-EWR-YQB
Day 2: YQB-ORD-XNA
Day 3: XNA-IAH-HRL-IAH-LRD
Day 4: LRD-IAH-BNA-EWR