Automatic change of Ship to location in PO

Summary:

Hi

Facing an issue in purchase order. we have 2 BPAs (BPA 1 and BPA 2) for same item, supplier and Requisition BU. However the ship to location is different in these BPAs (Location A and Location B) and different Buyers (Buyer 1 and Buyer 2) in BPAs

When we punch the line item in the PO ,the system always populate BPA 2. Even the location in the PO header is automatically changed to location B.

We expect to populate BPA 1 when we create PO with buyer 1 and ship to location A. And BPA 2 when we create PO with Buyer 2 and Ship to location B. Please suggest what is missing here.