Where minimum setback regulations are specific for a particular building envelope for a particular district, the following shall apply.

At a height not higher than the maximum base height specified for the applicable district, a setback with a depth of at least 10 feet shall be provided from any street wall fronting on a wide street, and a setback with a depth of at least 15 feet shall be provided from any street wall fronting on a narrow street. Such minimum setbacks may be modified as follows:

1. The depth of such required setback may be reduced by one foot for every foot that the street wall is located beyond the minimum required front yard, but in no event shall a setback of less than seven feet in depth be provided, except as otherwise set forth in this Section. To allow street wall articulation, where a street wall is divided into different segments and located at varying depths from the street line, such permitted setback reduction may be applied to each street wall portion separately.
2. The depth of such setbacks may include the depth of recesses or outer courts in the street wall of the building base, provided that the aggregate width of any such recessed portion of a street wall with a setback less than seven feet, as applicable, does not exceed 30 percent of the aggregate width of street wall at any level.
3. These setback provisions are optional for any building wall that either is located beyond 50 feet of a street line, or oriented so that lines drawn perpendicular to it, in plan, would intersect a street line at an angle of 65 degrees or less. In the case of an irregular street line, the line connecting the most extreme points of intersection shall be deemed to be the street line.
4. Dormers provided in accordance with the provisions of Section 23-413 (Permitted obstructions in certain districts) may penetrate a required setback area.