Perhaps with the images is more understandable, I would like to remodel the upper end of the lower plate so that it follows the curved profile.
I can't take a reference in the section....how do we proceed in these cases?
I don't think you can choose the surface obtained by dissecting the model (part or together it is).
try to disable the section, and choose the plan you want.
if you are in active together before the part you want to change.
do not take references in section even if you can at the moment then they are unstable
you should create an intersection curve between the section plane and the surface of the piece : at that point you can take the curve as a reference (split copy)
