[SOLVED: Look in Additional Information] I noticed that there was a sensitivity problem when the controller was on the customizable mode (without scheme, it's important).
Looks like the joysticks are 3-4 times less sensitive when in customizable mode.
I was playing before with an xbox 360 controller in the same configuration (without scheme, etc..) and there was no problem at all.
The problem applies to all the axes of the controller (cyclic, left/right pedal, and even the view in free look).
If I enable the scheme, then the sensitivity became normal (and probably a bit too much sensitiv).

This problem looks like this one : http://feedback.arma3.com/view.php?id=21926
But I can confirm that it's not resolved :/