In the - GAME OPTIONS/GENERAL/VEHICLE FREELOOK there is a setup (enabled/disabled) however, now after appearence of armor Interriors this setting does not will affect heavy armor vehicles. The activated FREELOOK will have influence only on planes, helicopters, cars, MRAPS - all vehicles in Arma3, but except only tanks and APC. This fact makes the setting of FREELOOK not stable for any vehicle in game. So player get different rules for free rotating the head inside vehicles.
When FREELOOK activated, then in planes, helicopters, civilian cars, light armored vehicles the player can rotate his head only by means Mouse, while inside the tanks and APC the player must use "Alt + Mouse" - this makes the player control not identical to all vehicles in Arma3, because after update 1.82 in the Tank and APC, the "Mouse rotation" is only the turret/optics rotation. All this moments makes some confusion for player relatively game settings.
As seems to me, inside heavy armor it would be better to invert this control.
The freelook must be - only via mouse, while the turret/optic rotation must be via Alt + Mouse.
If this will be done, then the "VEHICLE FREELOOK" could have the same effect on any vehicle in the Arma3, It would be logical.
Among other things, simple rotation of the head for a human looks more simple and natural action than the rotation of the turret or the optics of the tank inside. For this reason, this action should be easier to manage for the player control - only the mouse is the rotation of the head, while the Mouse + Alt (or any other button) - this is the more adequate rotation of weapons or optics inside the any vehicle.
Devs if you still are not going to invert it, then please, in the game settings give to the player any way to inverting this control or customized as desired. It still does not exist.
Any way to turret or optics rotation via "Alt (or any button) + Mouse" would be very desirable, while the FREELOOK would work just like in all other vehicles by means only mouse rotation. This is a main advantage of this feature - it would make the FREELOOK game setting the same for any vehicle in Arma3