When you advise to pay duty (Duty Y), we will check the import duty rate which one is the benefit between pay import duty or pay duty by FORM. Cause of some HS code if use FORM, it will has import duty rate more than without FORM.
However all shipment that you advise to pay duty it should has the FORM too.
Ex sample: HS code no.3204.17.00 that if use FORM AI, it will has the import duty more than without FORM.
Pay import duty by without Form = 0%