Hey brother .... My suggestion is to rely on the simple back-of-hand test. See how far your hand can be from the light without burning it. Thats how far the plant can also be
I hope this helps
close as you can get it to the plants as suggest above also have a fan blowing over the tops of the plants can get light even closer . to close burned . to far away they stretch and that's just as bad as burned in my book .