It's more of a mental thing. I have the same problem with good players. You're trying too hard. Don't use power swing unless you guess the pitch correctly. Also, and this may just be a placebo effect, but I've found against the computer I'll get more fastballs to hit if the guy is higher in the order but if you put him like seventh or eighth you'll get more breaking balls and stuff. The mental aspect is probably why I hit better with pitchers because I'm not trying so hard. I'm more loose. I see the ball better almost. Basically just forget Harper's so good and relax.