The height above the ground may have to be adjusted a little if you are signifigantly taller or shorter than the set target height. I forget what it is exactly. But you can calculate this in the same manner, you will feel if its too high or low as soon as you aim I guess.
For pre-made targets for dry-fire training Rink have some here: http://www.formgriffe.de/en/shpPfCnt.php?sCI=125 for pretty much every sport to print out and use at various ranges.. Just aim at the luftpistole one