I had an idea of using displacement to push the ground texture up as grass disappear due to distance from the player, so things hidden in grass would remain hidden.
It worked if I draw grass by brush or if I use Procedural Foliage tool for grass (which seems to have poor performance).
But if I use landscape material with grass node, the grass is pushed up, depend on the amount of the displacement (as the A on the picture)
Is there any way I can force the grass not to be pushed up (i.e. as the B)?