New Grower Mars 600 Watt

[grunge]

Hey Guys,
I am a first time grower. What should be the optimum distance of the lights from the plants for veg and for flower. As of now its hanging about 20 inches from the plant.
Also, how much space does the light cover ? With decent PAR.

Thanks in advance.

 

[AutoWonders]

When the seeds pops, I start my led light about 32", rolling down 22" or so over the course of one to two weeks.