Substrate Vertical Layer?

I can’t find any clear and simple answer, also not in the Documentation.

How can you use the Substrate Vertical Layer as a simple Blend node, with a simple blend between Top and Bottom Layer?

Just using a Scalar Parameter Value between 0 and 1 doesn’t work.
What do you have to do in order to create a simple Blend between TOP & BOTTOM Material?

Thx a bunch