Question on the Simhydraulics Poppet Valve Documentation and equation

I read the documentation on Poppet valve library block in Simhydraulics, and I noticed that the maximum area is applied when the opening signal passes the threshold value (h_max). But how does it know what h_max is?

h_max is not one of the input parameters, and also the documentation does not specifically explain how h_max is calculated if it were.