I spent 10+ years rooting clones and putting them in 6 inch pots to veg for 2 weeks then putting them into flower. They would only be 7-8 inches tall when they went into flower, and they would finish 25-30 inches tall and usually yield between 20-30g dried depending on genetics. I could fit 45 clones into a single 4x4 flood tray under a 1k hps in an air cooled hood.
yeah i did this i purchased a rooted clone PCG Pinnacle too be exact than i put it into 12/12 after a week of veg the root ball stayed super small it didnt fill out the 1 gal bucket it was in and i yielded around 10 grams. if you put a boat load of small plants into coco than flowered them you could get a good yield depending how much plants you put per sq ft.
I vegged one for maybe a week after getting a rooted clone home from my dad, & just popped it in a 2gal pot of coco and flowered it. Yield was terrible but it did all the normal stuff we expected of that cut.