Not sure I understand the question. All the stretching takes place under the screen, so it is hard to say how tall they are when they stop. The screen is 8" above my Blue Cheese, so that's as tall as they get. In terms or length, I would say they stretch 18" or so. Another way to think about it is that when I switch to flower, the plants fill 2/3 of the screen; the rest is filled in with stretch.
What size of a space are you growing in? Is the space in a small closet or a room? What's the ambient temp of the room as well. I've heard of heat issues with the internal balast systems. You may have to get better fans for a faster air exchange due to that balast being enclosed and giving off alot of heat itself.
I would get a clip on fan, set it on high and aim it up. It should definitely help, from my experience 5-10 inches is a little close, if it's hot to your hand underneath the light at that level it's hot to your plants. Happy growing!
THIS IS MY FIRST GROW WITH 250W HPS AFTER A FEW UNSUCSESSFUL CFL GROWS WHAT A WASTE OF TIME/MONEY AND EFFORT THAT WAS IM BUZZIN WITH THE OUT COME OF THIS GROW THE ONLY BAD PART BEING THEY HAVE BEEN FLOWERING FOR OVER 11 WEEK EVEN THO THEY'RE 8 AND 9 WEEK STRAINS 100% CLOUDY TRICHS A COUPLE OF AMBER ONES HERE AND THERE GONNA CHOP SOON 
at the beggining of flower it exploded with growth faster than the big bang i actually had this strain mistaken with bigbang for the first 3-4 week of flower coz the big bang was said to have explosive bud growth this strain has a spicey hash/skunk smell it has also threw out a few male bananas
right at the end of flower nothing bad tho just single ones here and there i just plucked em wiv the missus' tweezers i love the way this plant gives solid buds even on the lowest braches they are all solid im not keen on leafy bud prefer some solid nugz this strain stayed small i picked the 2 strains coz they supposed to stay relativly the same height i had to put the plant on a upturned bucket to give it some height there isnt much smell to this plant in flower yes it does smell of an apple cut in two but not much else really now in the later stages some purple has started to come thru looks kinda neat the buds have really swelled up in the later stage of flower my buds n this are kinda leafy not too bad but pretty leafy the other day the cola looked done i didnt check it for a few days and when i went back in the grow room the cola had produced a load of new bud growth and new pistils
the big bang is the one with the fatter cola on the left in the last 2 pics
when its dried il post some pics and smoke reporton these strains id just like to say THANX to all the members for all the help you have dished out to me and all and all the other people with sticky green finga'z 
