Patrick,
At first I thought you were talking distance to the hole so had the same response as Doug. I find the flat, 3 foot putt to be the most necessary to practice and perfect because if you cannot deal with that, you are not going to deal with any other putts. Perfect the straight 3 foot putt and the stroke will fall into place.
On your real topic, that is the 3 feet of elevation to the green, there is a course in this part of the world which takes that to a ridiculous extreme. Richmond Golf Club. Very, very flat terrain on a river delta and all of the greens are elevated 2-3 feet above the fairway. Problem is that it seems to reject almost every shot. The approach that takes a bounce in front and then on to the green will invariably roll off to the side, etc. I figure on a good day if you hit20% of the greens you are doing well. I HATE that place as a result. Not a bad layout, well conditioned but the 3 feet of elevation just ruin the course. I fully appreciate the drainage issue but the 3 feet must be used wisely and only some of the greens should be so elevated. No??
Bob Jenkins