I ADS all the time, I guess from years of playing FPSs with ADS Im just used to going in and out of it. Aim shoot, let go, run, aim shoot, let go, someones shooting you in the back, let go turn, aim shoot etc. after a while it just becomes automatic, I dont even think about it to the point where I cant really shoot while not ADS. I have to make a conscious effort to hip fire on people and its still hard for me.
Its impossible to track them??? try turning up your sensitivity.