When you reverse the calculation, you also change the source for the calculation from FOV 103 to 120, and if you're using 360 distance for hipfire you will get the wrong sensitivity for scopes.
If two scopes are the same FOV you would expect them to also have the same 360 distance, so they are identical.
Since you can change the Zoom FOV in QC it's quite easy to show what's going wrong. Here's I've set the Zoom FOV the same FOV as Ashe ADS:
https://www.mouse-sensitivity.com/?share=b5a237f18164a96df153c2ddcfe3f9e9
So the FOV and 360 of Ashe ADS and Zoom FOV in QC is the same at 40 vdeg and 82 cm.
But if you reverse the calculation, both will change to about 101.5 cm since you change the source:
https://www.mouse-sensitivity.com/?share=e621b3807a008120fd609a583691649d
So the scopes are no longer like you want them in OW2, but completely different. Using the same source is key to keeping the scopes the same between games. But yes, you will get some weird results when the hipfire FOV is locked, especially when it's very low compared the the other game.