Why Ongoing Charges / TER are different for Fidelity / HL?

An element of the charges are a fixed contractual percentage. The biggest component, for example, is the management fee at 0.85% of assets. Whether the fund grows or contracts its overall investment and cash portfolio (due to performance) or whether it gets more people to put money into it or more people take money out of it, they will always be charging the management fee at 0.85% ; an annual fee but worked out daily or weekly or monthly and perhaps more pounds per day at the end of the year than the beginning if the fund is growing.

The other costs, 0.04-0.06% (slightly higher on the income class than the accumulation class) will not necessarily be a fixed contractual percentage of asset values. They might pay their custodian or depositary a fixed number of basis points of the assets for looking after them, so if the fund size doubles the fee doubles. But if their auditor wants to charge £50k for reviewing the accuracy of a set of annual financial statements they will not suddenly change their mind and charge £50,100 if the fund size has grown by a fifth of a percent over the course of their review.

So, the actual total fees and charges which make up the running costs of the fund will be unknown and are estimated. If the audit fee is £50,000 - that is a lower percentage if the fund grows to £10 billion than if it stays at its current size of £8.5 billion or drops to £7 billion.

This is why the OCF Ongoing Charges Forecast can change from period to period. OCF is similar to TER total expense ratio. It is designed to be a measure of expenses as a ratio against fund size. If the fund size changes, not all the expenses will.

Examples of things in OCF besides just the fixed 0.85% p.a. management fee:

Audit fees;
Depositary fees & Custodian fees (including associated transaction charges)
Regulator fees;
Registrar fees;
Payments to legal and professional advisers;
Fees incurred in distributing income to Shareholders;
Fees in respect of publishing the price of the fund;
Costs of convening and holding Shareholder meetings;
The costs of printing and distributing reports, accounts and prospectus
Taxation costs of the fund;
Interest on and charges incurred in borrowings;
VAT is payable on these charges where appropriate

http://www.firststateinvestments.com/uploadedFiles/Content/UploadedLiterature/Manual/Emea/PdfProspectuses/Enhanced%20disclosure_First%20State%20Investments%20ICVC.pdf