Tris being drawed while not visible

I have game object that is just a container of some mesh grass, i'm using the Advance Foliage shader v4 from the asset store.

When viewing the grass i can see the tris count (120k alone for the grass) on the stats window, but i notice that if the terrain, for example a mountain cover the grass, and the grass is in front of the camera, but not visible, in the stats window i can see the same amount of tris.. If i disable the grass the tris count goes down.

I'm a noob at optimization and those things, so is this normal or shoiuld be addressed somehow?

Here are the screenshot showing what i mean: