Thanks, the effect works as it should now.
Last point in the same spirit, I recently redid my grass system without using "Forest Edge": unfortunately too heavy in terms of "parsing" time before rendering on Corona on extended scenes. So I try the old technique by increasing the density and resizing the "clusters" on the edges but it's laborious, you have to overcompensate for the general density of the Forest so that the effect on the edges can be achieved. And I have the impression that the computer overcalculating and then reducing the density in the center, which could cause slowdowns
I'm thinking of trying again with the effect for example, unless something escapes me and it's better not?