Yep, the low phosphorous was a theory I’ve been thinking of but I’ve seen pictures of deficient plants and their node intervals were longer. Though its very possible its a combination of both the lack of the nutrient and genetics at play here.
Using hydrobuddy, the calculated feed ratio for the mix is actually 1:0.48(P2O5):1.3(K2O). When I was designing the mix, I wanted to get as close to 2-1-2 as possible. Mainly because I believe that you don’t really need as much P, even in flowering. Another plus is that I can use pH down without worry since they’re usually phosphorus acid.