I attended a lecture very recently by a well known English professional wildlife photographer. The biggest thing I took away with me apart from memories of his fantastic images, was his advice to check the diopter of the eyepiece EVERY day that you are shooting, as ones eyes tend to change fom one day to another.
Sure enough, I checked my R9 and found that I had to reduce the diopter xx setting by a couple of notches. I haven't checked it since buying the R9 a couple of years ago!
It has made one heck of a difference to my own focusing skills! The R9 is very easy to adjust so just another daily check and so essential with a m/f camera.