Costs charged on each benefit payment

Annuities often charge administration cost as e.g. 1% of each annuity payment (during the payment phase). Generalize this to a cost factor with basis "Benefits". In the premium formula, this is an additional factor applied to the benefit PV, in the reserve calculation, this is a multiple of the benefit PV (or rather, a sumproduct of the benefit payments and the potentially non-constant cost factors)

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