Coaching has nothing to do with it, he cant tell how tight your sling is or what you see when you look down the sights. Fundamentals can only go so far, but theyre not a fix-all. The biggest variable is the shooter and whether he focuses.
Recoil of a bigger rifle will disalign all the little natural point of aim you had to begin with. It takes way too much time to renew the stability after every shot.
Then you also have to factor in the reload time.
Not only do you have to squeeze off 10 good rounds within the time frame, you have to rebuild that position 10 different times.
If you get caught up in the rate of fire and forget to breathe in and out after every round, you'll fall behind trying to calm down your breathing.
its simply a flimsy position for match grade timed rapid shooting. Sooner or later the left-right sway will get the best of you and your shots will be all over the place.