It depends on the pre-care you give. If you build the plant from day 1 to be the best it can be FOR A SCROG, than it can be quite low because the plant will be low and spread wide.
I top the hell out of mine AND do 4-way lst to build plants specifically to scrog. My frames are built at 15" so I can fit any plant in there. If one isn't as tall, put something under the pot to raise it to the camopy height.
1 plant. lst'd and topped-15" tall 42x42 screen day 26
