Side Yards. In the case of lots upon which an existing structure is located or which comply with the provisions for modification of subsection 12-7.2, combined total side yard requirements, as specified in Column 8 of the schedule of area, yard and building requirements shall be reduced by six inches for each foot by which a lot is less than the minimum requirement specified. In any case, the side yard area for either side yard shall not be reduced to less than 10 feet.