From my experience ( nikon d800+ 1,4 24mm et al) these focus problems- especially with wide angles with subject at a distance and wide open- are not easy to tackle.
If so Nikon- or canon should have done already. Also in low light things get more complicated. I have not adjusted any focus yet because at the moment i do not find any clear pattern. I try to use live view as much as i can.
On the other hand telelenses perform very well- the 70-200 is really fast and accurat...