STP-18: How is the supplier fee applied to the combination products? For example, for the On-Peak Jul-Aug16 combination, would the supplier fee be the amount for a single on-peak block or would it be twice that fee?

The supplier fee is applied to each Segment and month separately.  Thus, for the on-peak Jul-Aug 16 combination, the supplier fee would be twice the fee announced for a single on-peak block.