Any provision in this article to the contrary notwithstanding, if at the end of any fiscal year the total of the annuities paid from the retirement fund during the said fiscal year is more than ten percent of the sum of the balances in the fund at the end of the said fiscal year, the said annuities payable in the next ensuing fiscal year shall be reduced, pro rata, so that the sum of the annuities so reduced shall not exceed ten percent of the sum of the said balances in the fund. The said pro rata reduction shall be applied to all annuities payable in the said ensuing fiscal year.