>>707734tegaki being impossible to do that with maybe very well be part of it.
i have no idea how to get line smoothness that looks that good and infact might be entirely dependent on canvas size.
thats why i use a rough brush in my csp, i dont have to focus as much on making every line perfect and cleaning up sketches makes that even easier. an idea that i did forget to mention, i didnt think of it until a couple day after trying this method is that you still dont have to do everything on one layer, like the cross mapping facial features could totally be left on a disposable layer if its not adding anything to the image.
part of the reason i go for the sketchier messier look is from the mentality that cleaner shapes tend to make things look flatter since the brain doesnt process visual information in life with smooth edges in clear contrast so this works for me a lot.
but for getting something that clean with a smooth brush as well as the way i do it to minimize pixelation you really do need to work bigger so you have to view the lines from farther away. in any case line width/rendering your line work comes into play too, like if you really look into where her boob connects to her elbow on the left side you can see how the lines arent just meeting eachother but also sort of merging and going from thick to thin, its good to keep in mind that perfect lines arent everything, a lot of artists that seem to be making perfect images actually have some pretty messing line work if you really get down to examine it so just keep experimenting and see what works for you.