In the zlevel 5MM, the radius is being limited by the stepover limit. Raise the limit to 300% and you will get your 5 mm radius. This is to limit the amount of material left in the corners or between passes.
In the area milling steep, it should and just like Zlevel, but it looks like the radius is reduced to assure cleanup in the corner. I'm not sure where the 1mm radius is from.