Change in detail thickness on printed model when changing Outer Wall Inset?

[krikru 1]

I started tinkering with Outer Wall Line Width to see if I could print finer details by just reducing this parameter without having to change to a finer nozzle. I then saw the parameter Outer Wall Inset, and I tried to slice a few different combinations of these parameters to see what results I would get. For all combinations I had an Inner Wall(s) Line Width of 0.4 mm, except the one in last image for which I had an Inner Wall(s) Line Width of 0.2 mm, and I varied the Outer Wall Line Width  between 0.2 mm and 0.6 mm. Here are the printscreens I took of the various parameter combinations:

 

Outer Wall Line Width = 0.6 mm, Inner Wall(s) Line Width = 0.4 mm, Outer Wall Inset = 0 mm:

 

Outer Wall Line Width = 0.4 mm, Inner Wall(s) Line Width = 0.4 mm, Outer Wall Inset = 0 mm:

 

Outer Wall Line Width = 0.2 mm, Inner Wall(s) Line Width = 0.4 mm, Outer Wall Inset = 0 mm:

 

Outer Wall Line Width = 0.2 mm, Inner Wall(s) Line Width = 0.4 mm, Outer Wall Inset = 0.1 mm:

 

Outer Wall Line Width = 0.2 mm, Inner Wall(s) Line Width = 0.2 mm, Outer Wall Inset = 0 mm:

 

By changing between these images in the Windows Photo app, it is possible to see that for all the combinations with Outer Wall Inset = 0 mm, the outer edge of the outer wall are at the same position in Cura on straight parts of the wall (can be checked by placing the mouse cursor at the edge and switching image), so it seems like this is the "correct" edge placement. However, for the combination with Outer Wall Inset = 0.1 mm, the edge seems to have retracted by 0.1 mm into the wall, which will decrease the horizontal thickness of details (thicknesses of physical walls, circle radii, etc.) in the print preview by 0.2 mm, hence an incorrect thickness—i.e. a thickness that doesn't agree with the original 3D model (if we assume that the thickness of the details in the other combinations are correct since they all mutually agree).

 

How comes that the detail thickness changes when you change Outer Wall Inset parameter? Is this desired behavior? Or is the outer wall "pushed" out by the inner walls on the printed model (since they cannot occupy the same space), hence effectively outsetting the outer wall again by the same distance it was inset and leading to details that are just as thick on the printed model as when you use zero Outer Wall Inset?