how high should i hand my mh?

just putting in my new 400w MH/HPS, i have clones so how far should i put the light above them. they are about 4" tall and have 4 nodes. thanks for the input, and PLZ HELP

I started my 400mh light about 3ft up then moved it down slowy each day to about 18".
I suggest u let the clones grow some good roots before using MH as it will grow alot faster.

i got it at 2 ft right now, anybody else with suggestions??