How to unlock vegetation on the Z-axes


I’m trying to unlock vegetation placed with the vegetation tool. I can move objects on the X and Y axes, but for a lily for example, I’m looking for a way to unsnap the object from the terrain, on the Z axes.

I could for example, set a minimum height for the lily, but when I have several watervolumes on different altitudes that wouldn’t work out so well anymore.

I couldn’t find an option in the Editor, nor the parameters.
Can anyone possibly help me?

Oh - Disable : “grow on terrain” option.