Soft vs hard rails on weak and strong waves

I don’t understand what you’re going for here.   Every design element involves compromises and limitations.   Every combination of design elements invovles compromises and limitations.   We have a basic understanding of most of them, born out over 60 years of contemporary surf history and probably millions of surfers.    

When someone uses the term “hard” in a discussion about rails I am not thinking of the entire rail shape itself, but about the transition from the bottom to the rail.    Is that transition closer to forming an edge or a curve?