Where a vacant or developed lot is situated between two developed lots, the minimum front yard requirements of such lot shall be the average of the front yards of the existing buildings on the adjacent lots, except no front yard shall be reduced by more than 50% of the required depth, nor shall any front yard be less than 25 feet in depth, and further provided, where in a given block there is a pronounced uniformity of existing buildings where the front yard depths are greater than required, any new building shall conform substantially with the established alignment but shall not be required to provide a front yard depth of greater than 100 feet.