The gross area of a tract of land to be developed in a planned unit development district shall be a minimum of five (5) acres, provided, however, that smaller parcels may be considered on the basis of their potential to satisfy the objectives of this chapter as stated in Section 1163.01. When the planned unit development proposes a mixture of residential uses with commercial and/or industrial uses, the Planning Commission may limit the development of not more than eight percent (8%) of the tract to commercial uses and not more than twelve percent (12%) of the tract to industrial ones.