In all R3-TH Residence Districts the area restrictions and regulations shall be the same as those permitted in the R-3 Residence Districts, except that the average lot area shall not be less than 14,000 square feet; provided, however, that the Planning Board may reduce the average lot size from 14,000 square feet, but not below 12,000 square feet, appropriately as part of the site plan or subdivision review process. The calculation of the average as it affects certain land subject to the settlement agreement referred to above (§ 180-17) shall be in accordance with the terms thereof.