Don't worry about that :)
It was just that appear "evident" (for me:) to draw the chamfer directly on the Box for pick dimensions :D
I very well understand that will be a task to code that with any slowdown :)
So again don't worry with that :)
Each user can find his own way, who is inevitably not the same way of the conceptor :)
I can pick my points elsewhere on the grid for entiere dimension :)

Ps
The separate edges'curve for "Chamfer" works like a charm!
Just "re join" after and that's make the trick :)

Pss Silly Question : After a Chamfer or a Filet of an object "Show Points" don't work!
Is that normal? (I am a little tired with this winter / summer hours changes:)
I must separate again for show it!