I had to two conversion.
overwatch(fov103 hipfire)->PUBG(fov80-hipfire viewspeed) -> PUBG(scope - MD vs viewspeed)
then in PUBG, the viewspeed of all scope almost matched.(MD70.6%)
as you said, in insurgency sandstorm, the viewspeed of hipfire doesn't match each scope(each scope base fov is different)
gave up something method and I will use all scope MD0%
thank you and have nice day skidushe