I consider it a duck when there is a clear challenge which would be the best opposition to be made in a specific weight class a reasonable offer is made from one side and declined by the other, to fight a lesser challenge or cashcow. The alphabet straps have very little to do with it IMO. Mandatories be damned, they are largely a case of who has paid the most sanctioning fees.

Ducking example: Wonjongakam's career.