Understanding the cut away spacing

[LanceSA]

Hi All
I am very excited to build my own Thien Separator. I have watched as many YouTube videos as I can find.
But the one thing that puzzles me is the gap that goes around about 240 degrees. It seems that 240 is the magic number although I have seen all sorts of variants.

My question is why 240 as the base is supported by the top so why not 360 degrees?

[bbain]

It is designed like that so the air will create the spin in the chamber instead of under the baffle I do believe.  You want the air under the baffle to be relatively calm so it doesn't stir up the dust already there.