250w hps help

How hight should I.hang this 250w dual.spec in a reflector?

http://lmgtfy.com/?q=hps+height+chart

http://lmgtfy.com/?q="HPS+distance+from+plant"+site:rollitup.org

Don't.understand.chart.lol.

I use a 250 and keep my light '6 from the top of the plants.
About 6 weeks in to flower I push it to 4in away

I have mine quite high as I have a scrog in there will this matter?