Ah yes, lack of nutrition would do it. Coco has none so the plant needs it from somewhere else.Lots of things but primarily I think using coco and lack of nutrition in early seedling stage may have been the biggest factor, not had many other problems than that as far as I can see with my limited knowledge Definitely invaluable to see it done right and compare though your 100% correct.
I have two small clones from earlier in the year that I keep small for space reasons. One is in a SIP and the other is not for comparison purposes. The SIP plant shot ahead early but, since neither gets fed, they both knid of look the same at this point.
So that answered a question I had about whether it is just the SIP structure or if other things factor in.