Regarding LED focusing, I’ve had this thread bookmarked for a while now but I haven’t tried the technique yet:
I’ve also thought about getting a lux meter so I could at least do some trial and error to get the optimal focus for throw. But every time I think about buying one I end up just spending the money on a new light or parts instead, 
As far as artifacts, they can be due to many things like reflector design, LED design, reflector/LED compatibility, even things like reflections off the bezel causing rings in the beam. It can be maddening.