Problem subtracting alphas

I have two world aligned blends, one controls the height of the snowline, the other is where the rock faces are(where no snow should be).

The idea I had was to subtract the rock face blend from the snow line blend. The following image shows:

Top - snowline alpha
Mid - the rock faces (where I DONT want snow)
Bot - the result of subtracting the mid from the top. This is obviously not what I expected. Notice the bare valley of grass is now covered in snow.

Here is my material:

I tried using the Clamped input and various other things but none seemed to work.

I’m willing to try other ideas to achieve the same effect as well.