Induce Flowering, Height?

I was thinking of starting 12/12, my plants are various heights from 5-10 inches and I heard that during flowering that a plant will double in size, is this true?
I can only have them be 2 feet tall at the end because I am trying to keep my 1000 watt 2 feet away. I was going to wait till the tallest ones are 12 inches tall, does this sound right?
If anyone has experience with measurements of that I sure would appreciate some feedback.

Thanks!

Anyone.....

Yes, most strains will at least double in size after being put into 12/12. Some sativa dominant strains stretch even more than double.

just made sure there a decednt amount of lateral branches for bud sites. and let it veg so its nice and strong too, i go to like 18 inchea before flower

I usually flower when they are about 8-10 inches tall because I only have 32 inches of heigth. Well actually around 28 if you count the distance that my CFL takes up.

You want to wait 2.5-3 weeks on average before flowering. Different strains reach different heights so don't go by the height to determine when to flower. And they will double, even triple in height during flowering. If you bought the seeds online, they usually list how long the flowering period is.
More info would be helpful, including growing medium, strain, nutes, number of plants to lights, etc. 1000W light two feet away is about right; make sure you have fans blowing across the tops unless you're ducting the heat.

also depends on whether you're growing from clones or seeds
my NL from seed was vegged to 5 inches, about 5 nodes, stretched to 29 inches during lower
a clone from the revegged plant was vegged to 7 inches and 7 nodes, it stretched to 21 inches during flower
there's a lot of twists and turns in max height