After a tract of rural land has been granted rezoning to PR-4, the applicant may reduce the size of lots to the dimensions specified in this article. However, the total number of units permitted may not exceed 1.2 houses per gross acre. Freshwater wetlands as defined in the New Jersey Fresh Water Wetlands Protection Act of 1987, N.J.S.A. 13:9B-1 et seq., one-hundred-year floodplains, floodways and flood hazard areas are included in gross acreage for purposes of calculating units per gross acre.