I’ve completely reworked markup scaling in latest nightly build (revision 28258). By default, markup size is set relative to the screen size (does not change if you zoom in/out in a view), in both 2D and 3D views. Therefore scale is always reasonable, regardless of the size or spacing of the volume. I’ve also added an option to specify absolute physical size - then the markup size remains physically the same, so it changes as you zoom in/out in a view.