It's not the act of moving the stick that's causing the "head shift," it's Newton's law that "each and every action has and equal and opposite reaction." This means as the plane rolls right, your head, which has momentum, will want to stay where it is. Therefore it will "shift" the opposite direction of the roll.
Been on vacation, back now.
On the control stick issue, this IS 1 area where Newton's law (that you quoted) will come into effect as the pilot's body (object #2) will be applying a force to counter an opposing force created by the airflow being deflected across the control surfaces of the airplane (object #1). Simple leveraging can & will shift the pilot's body/head depending upon the amount of stick force necessary to properly deflect the control surfaces within a certain amount of time desired to initiate & hold said deflection.
As for the airplane during the roll:
This is Newton's law applied across an object #2 (pilot's body/head) thru/within another object #1 (airplane). When in straight & level flight momentum is applied EQUAL to both objects, thus object #2 (pilot's body/head) is considered NEUTRAL within object #1 (airplane). When object #1 (airplane) is rolled, the SPEED (degree per second) of the roll of object #1 (airplane) has to accelerate FASTER (generate more momentum) than the momentum imparted to object #2 (the pilot's body/head) during the roll for the "shift" to occur to object #2 (pilot's body/head) & this "shift" will remain until either 1.) the momentum of object #1 is SLOWED to match the momentum of object #2 or 2.) the momentum of object #2 is ACCELERATED to match the momentum of object #1 bringing both object's momentum back to NEUTRAL (realign both object's momentum--pilot's body/head moves back to center of airplane). We both KNOW it ain't case #2 (most of the time) that causes realignment. The pilot's body/head is NOT shifting due to opposite momentum (as you have implied in your statement) but is simply "shifting off-center axis" of airplane's vector due to an IMBALANCE of momentum applied between the 2 along the SAME axis of rotation (1 object rotating faster around the same axis than the other object that is located on the same axis).
It takes a fairly large deflection of the control surfaces to create the kind of momentum IMBALANCE to create a head shift during a roll (looking at this from a position of physics) as opposed to the physics generated from moving the control stick to deflect the control surfaces to generate said roll. Ever wondered WHY WWII German cockpits were so NARROW at the shoulder position? Guess what they were trying to control & why German planes tended to out roll all others & why their control sticks were so tall relative to others?
My post is not to question the dynamics in general (I don't question this) but to question the PROPER APPLICATION of the dynamics in-game & the only folks that can answer this post are the designers of the game, namely Hitech (thus why this post was originally directed to him). Since Hitech has actual flying experience as a pilot (mine comes from travelling in airliners as a passenger--which exhibits the same physics as described above BTW w/ the exception of the forces concerning a control stick), he can give better insight.
If Hitech chooses not to reply that is his perogative. Not gonna stop me from flying AHII.
Would like to see the head shift created from the proper physics being applied instead of using a distance of stick movement to "actuate" the movement alone.
My 2 cents.
