Inv approval driven by line-level PO matching instead of header-level

Summary:We are looking to modify our invoice approval workflow to be driven by
PO matching at the line level rather than the header level. The current
requirement is that all lines on an invoice should have a PO number. If
any line is missing a PO number, the invoice should go to the
requestor's manager for approval.
We also want clarification and
guidence on how this would work when an invoice is matched to multiple
POs or has partial matching (e.g., one or two lines are matched, and
others are not).

Here are the two failing scenarios we've encountered: