But no one said that the tangent was ALWAYS at 1.32 Vmd.
But if, as Alex and everyone else has pointed out, the curves are made up of an x squared and a one over x squared summed up then it is precise mathematics and not "conventional wisdom" that holds. I hope everyone is now quite clear about this.
Equally, I think everyone on this thread now understands how the mathematical result varies when Cdp and Cdi are not constants.
Dick W