Check if field is in a sublist of a record - Tricky Formula

Hello,

I am trying to write a saved search.  The intended result is to show me Sales Orders where an item is shipping from a location, that is not in a list of Partners {partner team member} on the customer record.

My thought was to create an array formula field, to dump all items from the Partner sublist of the customer, and then create a criteria to look and see if the Location is in that list.

(Of note, my locations and partners are used interchangeably, spelled exactly the same. )

Or, of course, maybe there's a slicker way to lookup the Location against a sublist from the customer record.