ME2DP- Down payment to vendor partner function

HI

We are facing a problem with vendor Down payment.

Vendor "A" is a main vendor created for Purchasing (MK01) having Partner Function vendor B (A.payment recipient-"AZ"). We raised an order to vendor A and trying to do Down payment against the same order to the Vendor Partner Function -B through Transaction ME2DP but system pick the vendor A not B for the down payment process. We have to change the vendor manually from A to B for every transaction.

Is there something we are missing? Please help.