CG is not an absolute number. This is more noticeable in gliders than in powered aircraft. I have no idea how it applies to helis or multi rotors.
Since I am primarily a glider pilot I normally set the CG at the specified point then go fly. I know it will fly at this position. Then I "tune to taste" to put it where I want it to have the glider fly the way I want It to fly. Usually I move it back from the starting point.
For my electric airplanes I do the same thing. Start at the given spec, then tune from there. However because you are flying under power virtually all the time it is not as critical unless you are a highly aerobatic pilot. For aerobatics I believe the tendency is again to move the CG back to make the aircraft more responsive to the elevator.
For trainers I think there is a tendency to keep the CG a bit forward to emphasize stability over maneuverability.
So, my advice is to set it per the instructions and "tune to taste."