Is there a way to inset in the ground the geometries instanced by the “landscape grass type”?
A parameter to say, make each model sink into the ground of this amount. Maybe with a possibility to randomize the amount.
This is because I am instancing stones and rocks and I would like to inset them by a little .
Any advice is appreciated!
Moving the pivot point of the mesh will do this, but not randomly, unless you make several meshes with different pivots.
Could you explain me how can I do that please? 
Would that work also with models from Megascan? I am importing several pebbles and stones…
As far as I know you can’t do that in the editor, so you either need to buzz over to Blender, or get something like this:
EDIT: I just saw another workaround for those not willing to part with time or cash:
“subtract a vector from the world position offset in the material. Then you can set it per material”
EDIT2: Incidentally, if you used the material method, then you could vary it with the PerInstanceRandom node…