When a variance or other approval for a residential use in that portion of the C-N Zone located in the Pinelands Area is granted by the Borough, Pinelands Development Credits shall be used for 50% of the authorized units for parcels under 10 acres in size; for 75% of the authorized units for parcels between 10 and 20 acres in size and for 100% of the authorized units for parcels over 20 acres in size.