The height of all buildings or other structures shall comply with the following provisions:

(a)        Except as otherwise provided in paragraph (b) of this Section, the height of all buildings or other structures shall not exceed 170 feet above curb level. However, such buildings or other structures may exceed 170 feet, to a height of 19 stories or 210 feet, whichever is less, provided that the gross area of each story located above 170 feet does not exceed 80 percent of the gross area of the story directly below it.

(b)        For the purposes of this Section, the Midblock Transition Portion shall be that portion of a zoning lot located within the area between 70 feet and 100 feet from the Madison Avenue street line, except for a zoning lot which has frontage on a wide street not located in a historic district. Within the Midblock Transition Portion, a building or other structure shall not penetrate an imaginary plane that begins above a line 100 feet from the Madison Avenue street line at a height of 20 feet above the height of a street wall built pursuant to Section 99-051, paragraph (b), and rises over the Midblock Transition Portion to a height of 120 feet above curb level at a distance of 70 feet from the Madison Avenue street line.