www.howtoairbrush.com you might find it helpful
basically the closer you are to the surface the thinner the line you can render
adjustments on airbrushs do not limit the amount of paint flow it limits trigger travel thus paint flow
if you are two inches from the surface and reduce the amount of paint you are putting thru the airbrush it will reduce the area covered but not define it any sharper as in rendering a fine line, the only way thats going to happen ( a nice sharp well defined line) to to move your airbrush closer to the painting surface while reducing paint flow both have to happen.
There is no adjustment on any airbrush that compensates for not spending time practicing dot, lines, dagger strokes the basic's.
have fun, its only paint