For each building within Subdistrict A, where the aggregate width of street walls is greater than 90 feet, a minimum of 20 percent of the surface area of street walls below the maximum base height and above the level of the first story shall be recessed beyond three feet of the street line. Portions of street lines with no street walls may be counted towards the recess requirements of this Section. No portion of such minimum recessed area shall be located within 30 feet of the intersection of two street lines. However, such minimum recessed area shall be permitted within 30 feet of Redfern Avenue, except at the intersection of Redfern Avenue and Mott Avenue.