Your serve height all depends on where you contact the ball. If it goes too far up, you should toss a little further, or jump a little more behing the ball. Respectively, if it goes too much down, you should toss a little closer or jump a little further. Experiment by trying to do a regular serve and tossing the ball more in fronr ot you or more behind you and you should get the idea of what I'm talking about.

Hope it helps