Yes, rescaling is always off. That’s why Victor asked me to multiply p4 by -1. The only way you could get a normalized quadbezier is if you call the routine by the corresponding number assigned to plugins by Csound (gen 65 in my machine). Even then, you’d have to call it as -65 to reverse the multiplication. Weird thing is that negative gen number means rescaling for quadbezier!
I think that in order to get the maximum height you should check for the greatest number in the arguments, i.e. y1,cy1,y2… That should work, shouldn’t it?