When you are outside of any vehicles and press RMB then you may see that mouse sensitivity decreases. It takes much more mouse movements to turn around then you don't press RMB.
I think it will be useful to make the same feature for joysticks. When you fly on helicopter you need more sensitivity but when you try to hit the target you need less of it - WY-55 Hellcat, KA-60, AH-9 Pawnee.
I think it will be good to make 2 different sensitivity curves:
first - x, y, z (like you may see them now in game)
second - x, y, z (the same but they will work only when you peer into the distance - press RMB, for example)
If your "first" and "second" curves the same then you will have the same sensitivity in both situations.