The director shall in accordance with his or her authorized regulations determine the portion of the aggregate amount of refunds and credits to employees made under Section 1176 during any calendar year which is applicable to voluntary plans for which deductions were made under Section 3260, such determination to be based upon the relation during the preceding calendar year of the amount of wages subject to contributions to the Disability Fund to the amount of wages exempt from contributions to the Disability Fund under Section 3252.