Nevermind i manage to get it working using a Fallout76Custom.ini file with:
[Main]
fIronSightsFOVRotateMult=2.136363636
[Controls]
fMouseHeadingSensitivity=0.005565
fMouseHeadingXScale = .021
fMouseHeadingYScale = .03738
bMouseAcceleration=0
fIronSightsPitchSpeedRatio = 1.0000
fPitchSpeedRatio = 1.0000
This seems to work on 16:9