Practice makes perfect. I did two careers with auto targetting. After a while there is no challenge anymore.
1000m or so are maximum firing distance for me although sometimes I have to try my luck at greater distances.
Your 4000m is admirable BillCar
I shot Orecarrier at distance of 5000m. Scored a hit to Auxilary cruiser at full 100% realism and no map update. But it had more to do with luck than skill. Can't complain though.