iternabe
I think in most cases this is a valid assumption. But just like acoustics, there are probably exceptions and also "no universal standard," same as keyboard height, key dip, etc.
I think where it's relevant is in the Fatar image, the "back of the black key" is at the bend in the white key. From an image of a (different) Fatar action, that would be a pretty tremendous gap to the fallboard:
For pivot length, I'm thinking it actually matters because of the unstated assumption that the accessible length of the keystick is the same, If it's not it definitely impacts the leverage that can be applied to the key.
My guess here is either the source diagram has some dimensional inaccuracies, or Fatar might be using a shorter key on this action (which is pretty common on synths, and even used to be common on acoustic pianos).
