In the Special Hudson Square District, the height and setback regulations applicable to C6-4A Districts shall apply, except that for buildings, or portions thereof, located on wide streets, and on narrow streets within 100 feet from their intersection with a wide street, the maximum height of such buildings shall be 290 feet. In addition, for buildings that exceed a height of 230 feet, any story located within the highest 15 percent of such building shall not exceed 90 percent of the gross area of that story located directly below the highest 15 percent of the tower.