Top and Bottom surfaces and impossible prints

[Tilleen 0]

I am trying to slice the Impossible 3d printed bolt and nut from Thingiverse.  The problem is that cura 3.2.1 does not seem to get the top and bottom surfaces correct between the nut and bolt. It seems to get confused and slices the top surface of the bolt and the bottom surface of the nut to be infill, and then puts the top/bottom surfaces further inside them.

 

I assume it is not treating the small gap between them as a proper gap?

 

Is there a setting that I am missing? What is the smallest gap it can handle?

[Tilleen 0]

I think I have found the option. It is Ignore Small Z Gaps. Needs to be off.