I was referring to them in the possession phase rather than in the defensive phase. My expectation would be an inverted fullback on defend would (depending on other roles) create a back 3 in possession albeit I accept it maybe would end up being its own role if that is not the correct nomenclature.
Edit to expand if not clear: I appreciate you can set up a 2-3 in possession but I was asking/hoping you would be able to set up a 3-2 shape.