Invoice Reduction for partial deliveries

I was trying to enter an invoice w.r.t  PO through MIRO using Invoice reduction layout. I am following a workflow to verify the invoice reduction scenario. Under this scenario two accounting documents are generated - Invoice for the delivered quantity (lesser quantity than the quantity in the PO) and a credit memo for the excess

Here are the steps I followed.

1. Created a PO for 100 items
2. MIGO for 60 items
3. I verified that neither the Vendor nor the PO has the "GR-based IV" checked.
4. When I do a MIRO the item quantity does not match that of the PO (100), instead the quantity shows up as 60.

Shouldn't the quantity be taken from the PO as I am entering an invoice w.r.t to PO? I selected the "Invoice reduction" layout but the quantities remain same.

Are there any other settings that I have to change?