Invoice account

Hi,

I want to use vendor invoice account for purchase order. I have a sub vendor X , where the invoice is Account is Vendor A.

However, for now, the on the PO header created for the sub  Vendor X, the price and discount sections are defaulting from the main Vendor A form (invoice account). I want that the price and discount section to come from the sub vendor X. But of course keep the invoice account as Vendor A so the PO invoicing will be against the main vendor A.