Some good suggestions here. If your middle finger is your dominant finger, (mine is too), your span may indeed be too long, or there may be too much angle, you might just relax the pitch in your middle finger only just a tad and see how that works. Sounds like your finger is just really hard against that edge and especially if you use grips, that repeated friction will get you. Adding some reverse pitch may be the quickest and most "non invasive" change you could make. The thing that sucks about adjusting fit is that you change feel at the same time, and quite frequently you can end up with worse feel out of a ball that technically fits better. Trying this change first may fix the fit without screwing with your feel.