The city and the retirement committee shall develop a schedule of investment costs relating to the investment of the funds in each of the accounts in the Firefighters Retirement System Fund, which costs shall be paid out of the funds in such accounts or assessed to the firefighters as provided in such schedule. The schedule of investment costs shall provide for the allocation of the administrative or record-keeping costs of the various investment options available to the members of the retirement system and shall assess such costs so that each member pays a fair proportion of the costs based upon his or her choice of options and number of transfers among options. All other costs related to the general operation of the retirement system established pursuant to sections 16-1020 to 16-1038 and not allocated or assessed pursuant to the schedule of investment costs shall be considered administrative costs and shall be paid by the city from the unallocated employer account.