The underlying height and setback regulations applicable to a C5-1A District shall apply except as modified in this Section. The street wall location provisions of paragraph (a) of Section 35-631 shall apply to all street frontages. For zoning lots that do not contain qualifying affordable housing or qualifying senior housing, the gross area of each story located completely above a height of 170 feet shall not exceed 80 percent of the gross area of the story directly below it.