Small-cap mutual funds are showing less staying power than midcap funds as the market pullback takes a bite out of the stock market’s 10-year performance. The average small-cap mutual fund rose an annual average of 7.94% in the past 10 years, and enough to turn a $10,000 investment made on June 30, 2005, into $22,527 by Sept. 18 this year, according to Morningstar Inc. data. Small-cap funds have fallen 7.5% since March 31.