How do I manually adjust amount I can flatten the curve for dark areas?

Hi Adobe Friends,

I am enjoying using the preset that comes with Lightroom called 'lift shadows', this takes the start of the dark info of the curves and raises it by about a centimeter on the graph. It creates that flat shadows look. I would like to be able to adjust the amount it raises the shadow lift. When you move the slider it just lifts the shadows up or down from the start point but I can't find a way to influence where the start point of the lift begins.

I would like to influence this start point as the 'lift shadows' preset sometimes lifts it too much and introduces to much noise in dark areas at higher ISO's. Any help in this regard would be appreciated.

Rich