(b) In computing the service charge permitted by this subdivision, if the premium finance agreement is executed later than thirty days after the inception date, there shall be deducted from the amount of such service charge an amount which bears the same proportion to such service charge, as (i) the number of days from the thirtieth day after the inception date until the day of execution of the premium finance agreement, bears to (ii) the number of days from the inception date to the date when the final instalment of the premium finance agreement is payable. No deduction shall be required under this paragraph, however, if the amount thereof is less than one dollar. For purposes of this paragraph the term "inception date" shall mean the inception date of the insurance contract being financed, or the due date of the premium being financed (disregarding any period of grace or credit allowed for payment thereof), which ever shall be earlier.

(c) Such service charge shall be computed on the principal balance of a premium finance agreement payable in successive monthly instalments substantially equal in amount for a period of one year. On a premium finance agreement providing for instalments extending for a period less than or greater than one year, the service charge shall be computed proportionately.

(d) When a premium finance agreement provides for unequal or irregular instalments, the service charge shall be computed at the effective rate provided for in paragraph (a), having due regard for the schedule of instalments.

(e) The foregoing charges shall be inclusive of all charges incident to the premium finance agreement and for the extension of credit provided for therein.

(f) The foregoing paragraphs of this subdivision four apply if the premiums under only one insurance contract are advanced or to be advanced under a premium finance agreement; if premiums under more than one insurance contract are advanced or are to be advanced under a premium finance agreement, the service charge shall be computed as if the premiums under each insurance contract were advanced or to be advanced under separate premium finance agreements.