This has been an issue since a lot of things, like opacity became sliders. Via stylus, if you don't grab the exact slider, it just doesn't work. Grabbing slightly next to it should grab the slider, but the extra area feels a bit small, tho this could be fixed with my next point. Tapping farther away is great for setting a value, however grabbing farther away from the scroll head doesn't do anything. This could be changed so that tapping still sets a value, but grabbing just grabs the sliders just like if you grabbed the slider itself. Just for clarification, when I say "grabbing" I mean click, hold and drag.