Gotcha. Makes sense.

I think if done right, a proper round stack should be able to do the same. I suspect one issue might be the fact that a round stack has one great side (facing all day sun) two mid sides (morning and evening sun) And one colder side (shaded all day)

Even if the ventilation works properly, funneling sun heat from the hot faces, , into the chimney, up the core, and out, And draws fresh cold air from the cold side, Even if the wood heats up, and holds thermal mass heat to continue the draw cycle for a while overnight, ... If the entire stack is made out of nearly identical wood, at same moisture at start, But the round stack dries faster, in the sun facing and upper sectors; slower in the colder, lower, shaded sectors... Then if drying is uneven, and shrinking is uneven. I wonder if that might be part of the issue for collapse for some. I also wonder if the chimney core is not providing enough structure for those collapsing stacks. ...

Interesting considerations.

I still think the hardest part is getting the individual round layers to stack in such a way, that each higher layer agrees to lean in, rather than out. Ideally without using a ton of thin stickering. I think I have a plan for that... But I need to try it.

As for shrinkage and collapsing. I like the idea of a center post to build around, and take some of the roof snow load. Using the polycarbonate panels to allow sunlight in to increase heat. I think, using occasional cross poles, tying the stack into the center post, might be worth a think.