Are the players in the game right handed? If the weapon is on the right side of the screen then more of the field of view is obscured on that side, same thing for up/down... down is obscured, up is wide open.
Reminds me of an old Battlefield where it was said input was fully linear start to finish, no smoothing at all, but the game gave an illusion of gradual acceleration by tilting the weapon more and more the further you got into a turn. Sounds like there could be more science like that in Rainbow Six Siege because of this left/right "problem".