Not sure what Cura does but outer dimensions are accurate while inner dimensions are completely off by 0.4mm (2x0.2mm) when using 0.2mm height with 0.4 nozzle. You can see by yourself already with a simple sketch in simulation mode. Make a square of 1.2mm perimeter. With 0.4 nozzle and 0.4 layer height you should have 3 lines side by side, but with with 0.2 layer height you should normally have only 2 (because material get squished on the side of the nozzle). Cura slicer is likely not accounting for that squish properly on the inside.
Using a 0.4 nozzle, we could probably attempt to solve i