Well, old topic revisited, but… _Testsetbackblendedge works pretty well (good enough for the girls I go out with anyway…)
Can we have options to set radii a and b independently?
Hello - Most likely the control will be for a setback distance (from the corner point) rather than trying to set a radius there - since it is not an arc. Does that make sense? Currently that setback distance is hard coded to some proportion of edge length or fillet radius or something.
-Pascal
Yes, I realise they are blends so eg a chord-length ratio would do it… 
Yes, in addition to the principal radius value, right? (1.00 in your example) 
Yes.
-Pascal
Perfect…
…when? Haha!