The regulations for permitted obstructions to applicable height and setback regulations shall be modified in accordance with the provisions of this Section.

For Quality Housing buildings, or portions thereof, as an alternative to the provisions of paragraph (c) of Section 23-623, dormers may be a permitted obstruction within a required front setback distance above a maximum base height, provided that the aggregate width of all dormers at the maximum base height does not exceed 40 percent of the width of the street wall of the highest story entirely below the maximum base height. Such dormers need not decrease in width as the height above the maximum base height increases.