Section 6O. A city or town may pay part of the premiums for group life insurance for permanent employees under the provisions of section one hundred and thirty-three to one hundred and thirty-eight A, inclusive, of chapter one hundred and seventy-five. The amount of such insurance for any employees whose yearly gross compensation is less than two thousand dollars shall not exceed one thousand dollars, and for any employee whose yearly gross compensation is two thousand dollars or more, such amount shall not exceed two thousand dollars. Any increase in the amount of insurance made possible by an increase in compensation shall take effect on the next succeeding policy anniversary, but no reduction in the amount of insurance shall be required on account of a reduction in compensation. Yearly gross compensation shall not include any overtime pay, and, in the case of hourly workers, shall be computed on the basis of scheduled required work hours. Fifty percent of the amount of any premium thereon shall be paid by the town. Any dividends or other refunds or rate credits shall inure to the benefit of the town and shall be applied to the cost of such insurance.