Hmmm, I have always just measured straight up from the ground to the center of the headlight while the bike is upright and me in the saddle (so obviously it helps to have another person but I've also done it myself). Put a mark on a wall 25 feet away at that same height measurement. Then put the light on high beam, sit in the saddle and aim the light at the mark. On high beam, I make the center of the bright region centered on the mark on the wall.
I get good illumination on both high and low and I never get flashed by oncoming drivers.
2018 Triumph Bobber with Triumph brown quilted seat, BC Sleeper Pros, Booster Plug, leather fork bag
2009 BMW R1200GS Adventure
2006 Harley Roadking