How do I default one segment of the PO-Matched Invoice Distribution Accounting String from Invoice?

Summary: I want to default 'Natural Account' segment of the PO-Matched Invoice Distribution Accounting String from the Invoice Amount and not on the basis of what is coming up from the PO Charge account . Other segment defaulting from the PO Charge account on the invoice is fine . So please guide me if there is any way to achieve that using Distribution Set or anything else . Thanks.

Content (required): I want to default 'Natural Account' segment of the PO-Matched Invoice Distribution Accounting String from the Invoice Amount and not on the basis of what is coming up from the PO Charge account . Other segment defaulting from the PO Charge account on the invoice is fine . So please guide me if there is any way to achieve that using Distribution Set or anything else . Thanks.