Look at smaller stations for guidance.

MHT/PVD/BTV/ALB/SYR/ROC - all mainline flights come in from and head back to ORD. these destinations have no other mainline service.

TUS - all mainline flights come in from and head back to DEN (TUS currently has no other mainline service)

In the case of SJC, there's mainline service to both ORD and DEN. So be careful, your inbound from ORD might turn around for DEN instead!