Height Lerp performs Blend Modulation. It takes the input “Transition Phase” and uses the “Height texture” to break up the input gradient. It looks to me like you are doing it correctly.
I have actually never used slope mask. Looking at it, looks like the ‘slope angle’ input is mis named. It should really be the Slope Vector, since all its doing is a dot product with that vector. Ie, if you want to extract all slopes you would simply use 0,0,1 for the vector there. Using 1,0,0 would allow you to select all the faces facing the X direction instead for example. Think of it more like a lighting mask to the direction you specify. Then the power and contrast just make the result sharper.