In any R zone, where the average depth of at least two existing front yards on lots within 100 feet of the lot in question and within the same block front is different from the least front yard depth prescribed elsewhere in this title, the required depth of the front yard on such lot may be modified. In such case, this shall not be less than the average depth of all existing front yards within 100 feet of the lot in question, or the average depth of existing front yards on the two lots immediately adjoining, or in the case of a corner lot, the depth of the front yard on the lot immediately adjoining. (Ord. 1212 § 1, 1969; prior code § 33.1001(D)).