That Soul Diesel is plenty big for only 56 days! In rockwool, going to rootbound is a fairly good thing. I just potted one up yesterday that was so rootbound that the root hairs grew into the microscopic pores of the plastic pot to the extent that I heard the pot tear from the root mass, lol. Of course in soil, you guys have to deal with transplant stress. Is there a tonic you can use to charge your girls up in preparation for a stressful event? For me, it's just a root inoculation with some bennies.
At any rate, I'd expect a pound from that SD as big as she is. Perhaps a phosphorus supplement from weeks 4-6 if possible?