Custom texture input for Landscape Grass Output

Hello everybody,
I am trying to use a B&W texture to drive the Landscape Grass tool in my Landscape material. I tried to connect the texture to a World Aligned texture, to a Landscape Coord and to Absolute WS, but the grass is created everywhere. I tested connecting the same output to the base color and to the Landscape grass output, (so it s the same texture), and I can see that the grass is created on the black parts too of the texture map.

I really need to deepen that. Could anyone help me to understand what I am missing?

Thankk a lot guys,