Re: Battlefield 4 low FPS when aiming down sights
In Nvidia GeForce Experience hover over Battlefield 4 icon and click Details. In Details section below you should see your optimised graphics settings that GeForce Experience set for you. In this window click custom settings icon and set slider to left at performance value.
See my screenshot below.
Don't forget to click Apply button and save your settings. After that, please check the game.
