Project Expenditures - How to tie the IPV from backend

Hello

Without PJM, we have PO inventory receipts tied to a project (expense PO distribution). exploring the below option..

1) I created the PO receipt transaction in pa_expenditure_interface and imported the PO receipts. Distributed the costs ..So far so good...
2) Now when there is variance on the AP invoice, PRC: Interface suplier costs (Invoices - Yes) is interfacing the full AP invoice amount as cost....

I want to know the link which ties the transaction so that PRC:interface supplier costs brings only the IPV to project expenditures....basically need the technicall link how Oracle ties PO to AP via project expenditures to customize...