Ref Discussion thread: https://forums.bohemia.net/forums/topic/239403-turn-in-or-duck-in-open-vehicle-turrets-such-as-humvee-with-stance-adjust-or-crouch-keys/

If a player is a gunner in an open turret vehicle, usually always is a "One burst Johnny", especially in pvp modes where life expectancy of gunners in open-top vehicles is a few seconds at most. Once rounds start cracking overhead there are no options to take cover, or even to brake line of sight other than scurrying to switch to an open seat or bail from the vehicle.

Suggestion is while in the gunners seat pressing the "Crouch button" or "Stance Adjust + Mousewheel down", player would let go of the weapon and tuck inside the vehicle.

Stance adjust would be ideal as players could just peek over the top of the hull to figure out where the fire is coming from before jumping back on the gun, with the lowest value of stance adjust having the character completely covered inside the vehicle.

Really hope this makes it into vanilla Arma games in the future.

-Thank you for reading