(a) There may be a provision as follows:

“Relation of Earnings to Insurance: If the total monthly amount of loss of time benefits promised for the same loss under all valid loss of time coverage upon the insured, whether payable on a weekly or monthly basis, shall exceed the monthly earnings of the insured at the time disability commenced or the average monthly earnings of the insured for the period of two years immediately preceding a disability for which claim is made, whichever is the greater, the insurer will be liable only for the proportionate amount of the benefits under this policy that the amount of the monthly earnings or the average monthly earnings of the insured bears to the total amount of monthly benefits for the same loss under all the coverage upon the insured at the time disability commences and for the return of the part of the premiums paid during the two years which exceed the pro rata amount of the premiums for the benefits actually paid hereunder; but this shall not operate to reduce the total monthly amount of benefits payable under all the coverage upon the insured below the sum of $200 or the sum of the monthly benefits specified in the coverages, whichever is the lesser, or operate to reduce benefits other than those payable for loss of time.”

(b) The policy provision in (a) of this section may be inserted only in a policy that the insured has the right to continue in force subject to its terms by the timely payment of premiums (1) until at least age 50, or (2) in the case of a policy issued after age 44, for at least five years from its date of issue. The insurer may, at its option, include in this provision a definition of “valid loss of time coverage,” approved as to form by the director, which definition shall be limited in subject matter to coverage provided by governmental agencies or by organizations subject to regulation by insurance law or by insurance authorities of this or another state of the United States or a province of Canada, or to any other coverage that may be approved for inclusion by the director or a combination of these coverages. In the absence of this definition the term may not include coverage provided for the insured under a compulsory benefit statute, including a workers' compensation or employer's liability statute, or benefits provided by union welfare plans or by employer or employee benefit organizations.