I'd have to challenge your analogy. We're saying to one side of the two-sided network that is our business that this is how much the participation of this participant's cardholders will cost you if you decide to accept the proposition. That's almost like a wholesaler saying this is how much these washing machines cost; charge what you want. That conversation goes to the acquirer, not to the issuer.
So the acquirer determines how much the merchant pays based on a wholesale price determined by a distributor, which is MasterCard.