is my light to high?

im on my second soil grow in a budbox growtent,on my first grow i had good success on my lower buds but my top colas were not as large as my friends were.another friend said the top ones had heat burns/stress on,i had the light about 20 inches away. well this time im worried about a repeat so i have put the light to the top of the tent which makes it roughly 6 foot in the air.my plants are in the 5th week of flowering and are roughly 4 foot tall (the tallest ones) but i also have 2 which are about half a foot shorter so this is why i have raised the light so i dont have the burn again.will this gap between the lights be too much or will i be ok? all advice and replys will be gratefully heeded

What kind of light?

sorry i didnt put that info! its a 600w hps light. and to be honest it seems like it has lost some of its brightness its on its 2nd grow schedule.im considering dropping it back down but my leaves are nice and dark green and the plants look mega healthy,i dont want to burn the tops this late in the schedule.by the way,my plants are a kush,how long should they be flowering for? mine have been for 5 weeks now,i thought i should start adding p.k in 2 weeks time for a week then flush them for 2 weeks with straight water.im pretty new to all this as you can tell!

I have been told my 400w HPS can be hung as close as 6 inches, however canopy temps exceed 80F when it is hung even double that distance!

Jorge Cervantes recommends 18-24" from the top of the plants for a 600W bulb. I do about 16" to 18" in my grows. Good luck!

put the light as close as possible. If you get heat stress, back it up a couple inches.