If it is a principal building where the gross floor area does not exceed 6,000 square feet, it shall then be set back at least 60 feet from the front lot line and at least 40 feet from every other boundary line of the lot. However, if it is a principal building where the gross floor area exceeds 6,000 square feet, it shall then be set back at least an additional 3% of 60 feet from every street line and at least an additional 3% of 40 feet from every other boundary line of the lot for every 1% which such gross floor area exceeds 6,000 square feet. In addition, if the lot on which such building is located has a bluff which is adjacent to tidal water and which has an elevation of over 10 feet above mean high water, then such building shall be set back from the top edge of the bluff at least a distance equal to twice the elevation of the bluff above mean sea level; provided, however, that the Building Inspector may permit a setback of less than twice the elevation if the face of the bluff is covered with well-established, dense vegetation and the toe of the bluff is protected from wave erosion by an artificial or natural barrier, and further provided that no building shall be located any closer than 50 feet to the top edge of the bluff.