brush rotation settting is totally off. it doesn't work as it has to.
the art marker has slanted nib. it means, that at some rotation degree the nib will draw bold line, and in that position the perpendicular line will be hairline.
if you hold the pen in that way, and you don't rotate THE PEN BARREL around its axis, just change the tilt, the pen has to work the same, it has to draw the same line. because the slanted pen won't change just because you tilt from another direction.