Oracle IDR - Non Matched Invoice for Suppliers with multiple sites

Summary

How does IDR determine the appropriate site when the address on the invoice is the same?

Content

We have encountered scenarios where one Supplier deals with multiple Business Units.    Our supplier setup is as follows:

WONKA CHOCOLATE FACTORY

We have one address:  123 MAIN STREET, TORONTO, ON M5X 8P9

We have 2 sites - neither site is marked as primary pay: 

SITE 1 - SITE ASSIGNMENT BU CANADA,           SITE 2 - SITE ASSIGNMENT BU USA

When a non-matched invoice comes through IDR the Supplier Address is the same for all invoices (123 MAIN STREET).

The only difference would be the bill to address which would have the Legal Entity Name and address.