The ADS isn't accurate, for me, I have ensured that my settings (independent, relative etc.) match in-game.
I'm in game trying to get a perfect 1:1 ratio for Hipfire : ADS, I test it by doing a 180 turn in-game with just hipfire, I then try to return to the original aiming point by going the same distance with my mouse while ADS.
But With 1.67 on the multiplier I overaim quite a bit & at the default 1.00 I underaim considerably, I'm going to try to find the right values in game.
The calculation I did to get the values are shown in the image linked below
https://i.imgur.com/4j5jJhV.png