Rhino seems to double the intended lineweight of an object’s edges when a corner edge is viewed other than at a contour edge.
This matters most at thick line weights.
This matters most at thick line weights.
That is due to working in a shaded view. A portion of the line thickness is occluded by the shaded mesh. In wireframe or ghosted mode you should see full thickness for those curves
In Rendered mode (which this is) is where consistent lines might be of highest value. 