Posting Purchase Order

Hi All

I have one Scenario, i have the PO of 10 Qty with Price total 10 (unit price 1), i receive the 5 partial deliveries each of the qty 1 and amount 1. Now i want to make the payment for the first 4 Deliveries, so i book the Invoice Registration for amount 4, and then i go to the Invoice Pool select that voucher then select the PO.Then on my right the sub total amount what should i get 4, the amount i book or the 5 based on the packing slip as i have received the 5 packing slip of amount 5. I think 5 based on the packing slip. Now from the match product Receipt i select the four packing slip, and click ok, now what should be the the subtotal 4 or 5. I think it should be 4 as i have select the 4 packing slips.

I have confusion in this, please advise me.