There seems to be a minor increase, but you probably have two things working against you. The hardest hit ground balls may get through, but the softest hit ground balls can also more easily turn into hits when compared with the typical ground ball. Plus, line drives often get caught while lots of bloopers fall in front of the outfield. Hitting it hard works best for SLGing purposes and especially for HR. But in a league with near elite defenders all over the diamond, plus defensive shifting in play, it makes sense that it would not guarantee a higher BABIP.