3mm section with 1mm line - no internal perimeter

[marcosscriven 0]

I have a model with straight, axis-aligned 3mm sections that I'm printing with 1mm line width.

 

These sections have only two lines in Cura output - i.e. just the 2 perimeter lines.

 

However, if I set line width to 0.99, then suddenly I get the expected three lines. I know I can turn on gap fill, but it seems to me there's some implicit tolerance or rounding going on in Cura.

 

The model in Fusion 360 definitely defined the section as 3mm, as as it's straight and axis-aligned, I don't see why Cura needs me to slightly reduce the line width.