Park 1221, throwing offspeed when you're ahead 0-2 or 1-2 can be effective if you locate your pitches. How did you get to 0-2 or 1-2? Was it with fastballs or offspeed? Maybe fastballs are all that you need especially if it has movement and you can locate up/down/in or out and hit your spots. Then again you said they throw first pitch fastballs 90% of the time. Of that 90% what is the % of first pitch strikes and getting ahead of the hitters? Remember in baseball good hitters make outs 7 out of 10 times.