The fund currently sits at just under $17 million and was New Zealand's top performing retail fund in 2009 and 2010 and has a five-star rating from Morningstar.

Pie Funds managing director and founder Mike Taylor said the $20-$25 million figure was decided on as "that's our best estimate as to a level where we could close the fund and still allow some room for organic growth."

He said setting a higher target would inhibit the strategy for a lean, nimble fund.

"Our investment strategy is focused on a concentrated portfolio of hand-picked smaller companies and we believe that in order to maintain our outperformance we need to restrict the size of the fund."

"If you grow too big, the performance suffers and you end up being substantial shareholders in your investments. We want the fund to stay nimble and the best way to do that is to restrict the amount of money you manage."

The Morningstar co-head of research Chris Douglas said that while soft closures were not unusual, the $20-$25 million limit was "very low."

He said that "while quite a few funds have caps" they were usually above the level set by Pie funds.

Taylor acknowledged that such soft closures are usually at larger funds but that, "Pie is focused on achieving the optimal performance for our clients, rather than collecting fees off a large fund, and we believe that restricting investment at $20-$25 million is acting in the best interest of our clients."

Taylor also denied the closure was a marketing ploy.

"We're so close anyway [to the limit set] when only talking about a couple of million, it's not a marketing ploy."

The Pie Australasian Growth Fund was launched in 2007 and has provided investors with a return of over 90% net of fees (but before tax) since inception.

The fund started with around $3 million and despite the Global Financial Crisis has grown thanks to performance and new investment money, and Taylor said he was confident the remaining allocation would be filled relatively quickly.

Pie said it has no plans at present to launch a new product, instead focusing on consolidating its Australasian Growth Fund.

However, Taylor said they may consider a new offer later in the year, dependent on client demand and whether they believe they can deliver an edge.