The best way to convert your BF3 setup to BF4 without using USA (if you don't want to use IRNV scope and stick with Kobra/red dot, and you don't like the USA procedural aim transition) is to work with the same monitor distance you have been effectively using in BF3.
Since BF3 uses a fixed 0.5x multiplier for the Kobra sight, and a fixed vFOV value of 40 degrees, this monitor distance is dependant on your hipfire FOV, and you can use the calculator to figure this out....
example, if you were using 90 Hdeg 4:3 FOV hipfire in BF3, you were effectively using a vertical monitor distance of 47.12% (as this results in a matching sensitivity value)
You would then need to set the monitor distance in BF4 to 47.12% to give the most similar feel at the slightly less zoomed in Kobra in that game. Example, using the above sens and FOV.