I ballasted it to 700g (8 slugs over 10), which means that the ballast provided (900g) won't be enough in strong conditions, so there is a need to ballast in the joiner. Fortunately I have 2 tungsten ballast slugs remaining from a previous plane, so I will be able to add 500g more, so a total of 1400g, not that bad.
I moved the CG to 108mm, and thank to the fine tuning function of the T12FG, I played with the amount of snapflap.
I ended the day with the current settings:
(Note: + means "Down", - means "Up". Ailerons and flaps measured at the junction, elevator and rudder measured at the root)
CG: 108 mm
Elevator: +/- 5mm
ailerons: -1 mm
flaps: +45 mm
ailerons: -18 mm
elevator compensation: +4 mm
Here is the last video I edited: