Payables: How to Enter a Credit Note to Reduce Price as an Adjustment Voucher

I have a question about Payables Adjustment Vouchers and Matching:

Suppose that we order a quantity of 4 at £100 each, the supplier delivers 3 but invoices us for 4.  I understand that, if the supplier then sends a credit note for -1, we can enter the credit note as an Adjustment Voucher to reduce the combined Voucher (Invoice and Credit Note) quantity and amount to match the Receipt quantity and amount.

Now suppose that we order a quantity of 4 at £100 each, the supplier delivers 4 and invoices us for 4 but at £120 each.  If the supplier sends a credit note for -£80 (4 x -£20) can we enter the credit note as an Adjustment Voucher to reduce the combined Voucher amount to match the PO amount without increasing the combined Voucher quantity so that it no longer matches the PO quantity?