ok, that means ironsights/1x optics have a 0.9 fov multiplier and a 0.6 sens multiplier.
imho it's best for muscle memory when fov multiplier and sens multiplier are identical.
in order to achieve this the calculation is:
0.9/0.6/0.02=75
AimDownSightsMouse=75
XFactorAiming=0.020000
the only difference to csgo is that r6 siege uses vertical fov, whereas csgo scales with horizontal fov based on 4:3, but the difference is miniscule.