Here is trick I picked up. Wrap a piece of tape around the end of your airbrush making a tube. This will catch the paint and cause it splatter off the end of the tape. You can also use a piece of plastic or rubber hose to achieve the effect. Of coarse air pressure and tube length/diameter will all have an affect. It seems way easier to control the placement of the spatter this way. Experiment and see what works for you.