A. On a site situated between sites improved with buildings, the minimum front setback shall be the average depth of the front yards on the improved sites adjoining the side lines of the site.

B. Where a site is not situated between sites improved with buildings and where sites comprising forty (40) percent of the frontage on a block are improved with buildings, the minimum front setback shall be the average of the existing front yard depths in the block.

C. On a site which is not rectangular or approximately rectangular, or is a flag lot, the location of the required front setback shall be determined by the Director.

D. In any R District where the natural grade of the front setback of a lot has a slope such that it is not practicable to provide a driveway with a grade of fifteen (15) percent or less to a private garage or carport, the garage or carport may be located within the required front setback.