I want to raise a newly created unit out of the ground.

I've tried it using behaviors only. -> Fail, behaviors can't have a negative height modifier

I've tried using a behavior that lowers the unit at start and raises it afterwards. -> no height change (wtf?!)
(To be exact, I've used 2 behaviors for that, but the height effects aren't )

I've already had huge problems with raising and letting a unit fall down with a behavior and modify height effects. With a workarounds (e.g. apply modification a 2nd time) I could make it work.

Even the trigger action modify unit height can't sink a unit into the ground...

BUT is there a way that makes the data stuff work like it should work?

I guess this is a bug on Blizzard's side. The unit's raise & fall started to bug when Blizzard applied an item's height "fix".

You can make the unit's height a negative by default, in the Data Editor. Then use triggers/behaviors to add height to it, giving it the illusion of coming out of the ground.

That is what I have to do now.

The sinking won't be visualized, if the heigth is below the ui heigth. But you have to raise the unit back to normal level even if the sinking isn't visual.