If the high ball is catching you off-guard--which it sounds like it is if you're dropping it short--then pay attention to these two things when anticipating your opponent's next shot:
- Your shot quality (the ball he has to hit)
- Your current court position
Chances are, you're hugging the baseline too closely when hitting him low quality shots. Then, a deep ball comes back, you're too far in to return it properly, you start to backpedal, the ball gets up high on you, and you're hitting the shot off your back foot--maybe even while moving backwards!
Make sure you're in the right court position to return the shot that is likely to come back, set-up early, and make sure you're moving your body into the shot
. If you're in the right position, and get set up in time, you should start seeing those shots penetrating the court more.