i have 3000 hours in siege and i have tested it all. fov has no influx on siege sensitivity. i have no handcam and sens matcher doesnt appear to be working in siege for me just now. else i would have send you the clip. (i actually just found a way, very unfomforable one nevertheless. but proves my point)
siege has weird sensitivty system, ads is fixed percentage of speed (depending on the ads setting), xfactor is a fixed percentage of speed applied on the ads speed.
so by putting your xfactor on 1, it makes the acog, glaz scope, kali's sniper scope (no matter what magnification), same as your 1x scope sensitiviy (which you can regulate by changing your ads speed).
this a better view of what it happens if you apply it with glaz scope and acog.