In C1 or C2 Districts mapped within R9 and R10 Districts, or in Commercial Districts with a residential equivalent of an R9 or R10 District, for zoning lots containing a building that is developed or enlarged pursuant to the applicable tower regulations of paragraph (c) of Section 35-632, the provisions of Section 23-241 (Special tower provisions) shall apply:

(a)        to only the residential portion of a building where less than 75 percent of the total floor area of such building is allocated to residential use; and

(b)        to the entire building where 75 percent or more of the total floor area of such building is allocated to residential use.