Invoice approval across Operating Units

Hi Pros

We have the following scenario:

-Users can raise Requisition across different two OUs and approval can be done by users across the OUs

-Once PO is generated from approved Requisition, the AP invoice is matched to the PO (2-WAY Match)

- When invoice is sent for approval, only users of the OU where the PR was raised are found in the LOV for invoice Approval.

-We use AME rules for the invoice approval hierarchy.

Question: What can we do so that users of both OUs are found in the Invoice approval LOV?

What HR profile option controls this functionality?