Getty Images Shutterfly is among a group of small-cap companies with declining forward price-to-earnings valuations even after tremendous gains.Small-cap stocks are this year’s best performers, but there are still hundreds whose valuations have declined this year, making them potentially attractive investments. Small U.S. companies derive a greater share of sales and profits domestically than their large counterparts do, so it appears that earnings estimates haven’t yet caught up to the post-tax-cut reality. The reduction in the maximum federal income tax rate to 21% from 35% for companies certainly is a game changer, especially for smaller ones that lack the complex structures that can help large ones greatly reduce their taxable income. A company that was paying the 35% rate before the tax cut would enjoy a 22% boost to after-tax earnings, all things being equal. We’ve screened small-cap stocks whose forward price-to-earnings ratios have declined despite big gains in the market. But, first, here’s how valuations for the three main S&P indices have changed over the past year.via