And the FMA's KiwiSaver Tracker tool, which correlates fund return and fee data, shows "no clear link between higher fees and higher returns, apart from a couple of standout funds".
FMA director of regulation Liam Mason says that's the message the organisation is trying to get out to investors — they need to make active choices about their fund.
"We don't see a strong correlation between fees and returns, but we do see a relationship between fund choice and return."
He says the FMA hopes the advent of two low-fees providers — Simplicity and Juno — in the market will move the dial in terms of fees overall.
Juno doesn't charge fees for savers aged under 18, and has a graduated structure, so savers with lower balances pay lower fees.
Another concern is whether KiwiSaver providers are lowering fees as the total amount of money invested increases.
Total KiwiSaver assets rose to $48.6 billion this year, and there are now 2.8 million members, up 4.2 per cent since March 2017.
Mason says part of the FMA's work plan is to look at how fees paid by Kiwis stack up internationally, and to check if the definition of an "unreasonable" fee in the KiwiSaver legislation is fit for purpose.