When Proximity Routing is enabled, the UPS eFulfillment Portal will look for available Warehouses that have inventory. Your "Main" warehouse location can be used as an available Warehouse if you have the address information filled out for it and if you have quantity available.
The logic for routing is:
1. Which Warehouse can fulfill the order in its entirety
2. If there is more than one Warehouse that can fulfill the order in its entirety, then it will route to the Warehouse that is closer to the buyer.
Routing is enabled through step 3 on your Wizard
1) Go to the ADMIN menu -> Shipping Rules.
2) Click on the overlapping arrows icon.
3) Click on the switch next to the marketplace you wish to enable proximity routing on.
4) Click SAVE.
US Territory and international orders will continue to route based on the current PO Source rules.