i have had the screen anywhere from 6-18 inches above the soil. you just need to have enough room to get your hands under there to train them.

with my ww's i have to fill the screen 75% in veg, then go to 12/12 and the stretch takes care of the final 25%. i also have gypsy's kiss from reeferman which i have to fill the screen closer to 90% in vegg. every strain is different. you need to get used to how each strain reacts to the screen before you can get the high yeilds that scrog boasts. i finally got the hang of the ww's! with the gk's i have 2 different pheno's and am still messing around with both to decide which is better suited for scrog.