So if you run your game with the default (90) FOV, you will be fine and the tank's sights will be accurate. If you aim at 1500m with a target that is 1500m away from you, you will hit. But if you run a different FOV (like me with 120 FOV) your tank's sight will change and you will miss your shot. See video for more details.
PS In the video I change the FOV for demonstration, so the bug doesn't only appear if you change the FOV while sitting in the tank and spamming settings. It works all the time.
Steps to reproduce the bug:
- run 120 FOV, get into some tanks, let's say T-72B3
- Scope. Aim at long range target (to see the bug better) with mark on sight
- Fire
- Miss. Now your sight is not accurate.
- Change FOV to 90
- Unscope and scope again to see that the sight has changed its position and is accurate again.