"It's no longer a start-up. We're into the 10th year of the scheme so it's mature. It's operating and you do expect to see changes," Matthews said.
"It's a bit like a business, when it starts operating you're going to have all the growth and then eventually it reaches a more solid ongoing position and that's what the result suggests ..."
Member contributions to KiwiSaver schemes climbed 10 per cent to $2.6 billion and employer contributions rose 9.6 per cent to $1.6b, while Crown contributions shrank 21per cent to $728.3m with the end of the $1000 kickstart for new members.
Withdrawals jumped 56 per cent to $1.16b, with first-home purchase withdrawals more than doubling to $495.6m.
In the course of the year, 175,000 members transferred to a different scheme provider compared to 177,000 in 2014/15. In the same period 145,000 new members joined compared to 245,000 new members in 2014/15.
"As new membership is slowing, it's logical that providers will continue to look to transfers to grow the size of their schemes," FMA chief executive Rob Everett said. "The FMA will be paying attention to how transfers occur, making clear our expectations to providers and giving clear information to KiwiSaver members about how to prepare for those circumstances and what they should expect from providers."
The number of default members continued to decline from its peak of 465,000 in 2013 to 445,000 in 2016, now representing 17 per cent of total members.
Matthews said this reflected members taking a more active role in understanding their investment scheme.
"That's quite positive, because if people are not in a default scheme that suggests they are actually taking an active interest in where their funds are invested," Matthews said.
"So again that's a really positive development because it means people are becoming engaged with their KiwiSaver and making active decisions as opposed to just letting things happen ... If they're making active decisions we would hope that they're going into more appropriate funds for their situation."