OK so MAC (Main Aerodynamic Chord) is at 215.86 cm from center line and is 142.20 cm.
That means that the Aerodynamic Center (AC) for that wing is at 131.58 cm from the nose of the wing (25%).
Antoine that should be the starting point for the CG of the empty glider. I would expect that the CG point for all together in flight be around 125.4 cm from the nose and in the horizontal plane (20% of MAC or a 5% static margin).
These should be good numbers to start and should provide a flyable system. We can fine tune later.
The vertical position of the CG is whatever it is vertically from that point (125.4 from the nose, center line)