ArmA1 and ArmA2 have different sensitivity to a freetrack, actually I have to use different profile with different sensitivity and curves for these games(while ArmA3 feels the same with ArmA2). So there seems to be some vaule of sensitivity in the game after The trackIR\FreeTrack interface, and this is the vaule should be changeable.
And maybe more reduce for a powerd 3D-Scope, since it's even harder for a HeadTrack user see: http://feedback.arma3.com/view.php?id=10373