They are made with very little paint by pulling the trigger only slightly back of your airbrush. But when your paint is very heavy and dark its very hard to do a low intensity dot.
Reduce your paint so it gets more transparent. With the reduced paint its much easier to get all kind of intensities then. If you wanna have a darker dot just layer some more
layers over the spot. But becarefull not to spray too much at a time, give it time to dry and build it up slowly.