Also,....it's not such a good thing to raise your light during flowering, unless you are using a big light, running really close, like a 1000 HPS at 10". You could get away with it then, but it most cases, you'd be sacrificing quality and yield, backing the lights off.
Look into bending them off to the side and tying them down, if they get too tall, too. That's pretty much the best option, for controlling heigth, during flowering, if they get too tall. How long since you flipped to 12/12?