During my practice stroke, for long putts, I hold my finish position at low point and then look at the hole. For some reason I can get a feel for how much thrust I need.
I completely agree Spike. It's becoming instinctual. Now when I look at the long putt, My body adjusts automatically to the distance. It wasn't like that at first. At first, short and medium length putts were easy but I had make a conscious effort to set-up up for longer putts.