At what level should sourcing rule be assigned in case of dropship scenarios?

Summary:

How to set up sourcing rule assignment for dropship scenarios - We cannot set up at item+Region level as there is a possibility that multiple BU will map to same address.

Expectation is every BU will have a different supplier site for same supplier, this combination of supplier + supplier site would make up 1 sourcing rule each.

How do we proceed with assignment so that correct rule is picked automatically?

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