Imagine all variables and custom functions are declared and defined in Awake, but called from within Update, or FixedUpdate for the physics functions.
If my understanding is correct, functions don’t do work until they are called, and Unity calls Update and FixedUpdate (and their content) by frame and by time respectively, and it is the priority with which Unity handles them (and their content) that makes FixedUpdate preferable for physics.
So if Update content calls only functions not related to physics, and FixedUpdate content calls only physics functions, why does it matter where the functions are described?