If you are going in a complete opposite direction i think some of the fundementals need to be worked on. Maybe you are getting there too late and contacting late which would change the direction to down the line.
How are your top spin shots? Another thing for lower shots is you should be closer to them rather than further. Your arm is connected to your body at the shoulder so naturally you will have less reach as the impact point moves lower. Therefore try getting close to that ball, not too close where you are crowding yourself but you shouldn't have to strech to hit the ball, as you will lose power and control.
I'd just work on top spin shots by rallying half court to get fundamentals down pat.
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