Upon rewatching the video, I realize the chimney wasn't mentioned in said rule. So the solarium juicebox one is not even an exception, 8in throughout, and then there is the chimney.
Yes, I do see batch box designs having mostly brick bells. Hm. So the double stacked barrel isn't an exception either, or more like, it's a different core so the rule needn't apply.
What I'm gathering is that the J tube desires a certain something from the rest of the system (like constant CSA / chimney close to barrel) to assist rocket-y airflow, whereas in a batch box with a strong venturi effect built into the core, the core is rocket-y enough on its own to allow some design variation? Does that sound about right?
Not that I will try to innovate or anything, I will definitely stick to the Wisner J tube design when I get to build one in a backyard. I just want to feel confident that I understand the stuff presented.
