The transparency requirements of this Section shall apply to the High Line frontage portion of buildings developed or enlarged after June 23, 2005, and located in C6-3A Districts and within Subareas A, C, F and G, except for such portions that contain dwelling units. At least 50 percent of the area of such frontage, to be measured from a point not lower than four feet and not higher than eight feet above the level of the High Line bed, shall be glazed and transparent and at least 75 percent of such glazed surface shall be fully transparent.