I feel like a bunch of people are skirting right around this but this was unclear to me. The design calls for an absolutely enormous taper at the bottom called

I feel like a bunch of people are skirting right around this but this was unclear to me. The design calls for an absolutely enormous taper at the bottom called the collector. That land area is covered surface, so there is a huge volume of hot air that isn't mixing around the column near the base. I assume this is how they get around the symmetry issues of a uniform cylinder. I had to go to one of the publications to find a close up photo with much clarity, maybe this will help others to notice.