I vegged my girls for 13 weeks with lots of training and defol, and I have an extra four feet of height. I have about 70 colas on three plants that aren't any taller than 18". I think there are many factors involved... strain, stress, light, root ball size and health... I got no more than six inches of stretch on any of the three strains.
The thing about scrog is that it undoes the plants natural tendencies with regard to height. And does height matter if you have a full, even canopy?
It amazes me how much there is to learn about growing a weed! Just as in life it's all about finding balance. More plants, shorter veg, requires smaller root balls, thus smaller pots. In that same space, half the plants require larger root balls, thus larger pots to support more of the same size colas filling that space.
"Seeds. Check. Dirt. Check. I think I'll grow a little weed" LMAO!!!