The light's brightness and where you are riding are probably more important than height. When I bought the Reelights from my son, they are designed to mount at the axle. I mounted them about mid-fork height. If he needs, he also has a light that attaches to his handlebars.
My mongo light on the SUB is mounted in front of and below my handlebars, but that is so I can reach the switch while riding.
What I have found it to not ride too far right, so whatever light you do have does not blend into the lights along the sidewalk (shops and such). Also, flashing mode will help separate you from other lights, as well.
I'm like you, I like unobstructed handlebars.