Hi Eric,
Like you say, it’s a choice. The Output of the Color Ramp doesn’t reach 1, because the white was changed into a grey. For a Mask you want black and white Values (and often not much in between). An alternative to the Color Ramp in this case, would be a Math Node set to Multiply by 10. This would do the exact same thing.
The Values then are between 0 and something around 9 or so, but the Mix Shader Clamps its Input (Factor) between 0 and 1.