For uses denoted with an “S” in Section 32-131 (Use Group III – general use allowances), the provisions of this Section shall apply. For any philanthropic or non-profit institutions, with or without sleeping accommodations, in all Commercial Districts, the number of persons employed in central office functions shall not exceed 50, and the amount of floor area used for such purposes shall not exceed 25 percent of the total floor area, except that in Commercial Districts mapped within, or with an equivalent of an R8, R9 or R10 District, 25,000 square feet, whichever is greater.