Mortgages must not exceed either the statutory dollar amount or loan ratio limitations established by the section of the Act under which the mortgage is insured, except that the Commissioner may increase the dollar amount limitations:

(a) By not to exceed 170 percent, in any geographical area, in which the Commissioner finds that cost levels so require; and

(b) By not to exceed 170 percent, or 215 percent in high-cost areas, where the Commissioner determines it necessary on a project-by-project basis.