Only a colour of 1+ will actually fully mask the stone, anything lower then that in the grays will just be flattening the stone down to nothing at (1+).
I don't know if that makes sense, so naturally here is an example. This is not an example of how to distribute stones, but just the difference between two density masks. Both have the same settings except their contrast, which makes the gradient falloff between low and high colours tighter.
Additionally, to this demonstration, changing the colour offset into the negatives, like -0.25 will give the noise more low colour than high colour, which would create further gaps between noise based on the lead-in scale.