If you have a HICAPS machine you can collect data every time a patient claims — the fund name, the amount charged and the amount of the rebate paid.
Over time this lets you build a profile and see which funds pay better than others. You can then let your patients know the average rebates to expect when they claim. Of course average rebates are only a rough guide. You must tell your patients that actual rebates depend on their level of cover, how long they have been with the fund and their annual limit.
One thing that shocked me was the variability between funds. For example one large fund paid, on average, 20% less than a much smaller fund.
As they say, knowledge is power.