C. For flexible premium policies, reserve liabilities for any guaranteed minimum death benefit shall be maintained in the general account of the insurer and shall be not less than the aggregate total of the term costs, if any, covering the period provided for in the guarantee not otherwise provided for by the reserves held in the separate account assuming an immediate one0third depreciation in the current value of the assets of the separate account followed by a net investment return equal to the valuation interest rate. The valuation interest rate and mortality table used in computing this additional reserve, if any, shall conform to permissible standards for the valuation of life insurance contracts. In determining such minimum reserve, the company may employ suitable approximations and estimates, including but not limited to groupings and averages.