Moving the CG will not make it "stall into a spin as desired"
This is a very popular misconception.
On any light , properly trimmed aerobat, the CG location works best about 33% - for precision flying NOT flailing flying.
When you add a little elevator at low throttle (idle ) , the model will simply loose speed and adopt a high AOA sink.
Th ONLY thing that will setup the spin entry as desired, is to learn to rather quickly (and sometimes holding in power ) bring the nose up as high as possible with out changing altitude.
IF the CG is proper or even better, a bit noseheavy, the stab will stall and the model will easily break into the spin.

For the spin to work as intended , you must also control yaw till the break is ready to begin --THEN add rudder .
Ideally the nose drop and rotation (one wing panel drops )will occur all at once.
This is how the spin is scored. -If the judges know how to properly score it.
restated :
You must have enough AOA to trigger a "break" -and not get caught in a mushing setup.
We use lots of elevator throw to set this up and learn to put it into effect as fast as possible wihout changing altitude.