It depends a lot on the C99 phenotype involved I think. I'm in a cab with a little over 4' max height. I switched when my plant was 12" and it grew to its final height of 27", so the space I'm in is perfect.
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this guy's grow, he had one plant go from 9" to 38" after the switch! Next time I do this, I'm going to try topping or fimming, so the canopy is more even and I don't have that single phallus sticking up through the center. If you account for the plant to triple during the stretch, you should be fine.