Airbrush Tune-up

Read an article in the March 2001 FSM yesterday by Robert Oehler called "Airbrush Aerodynamics", so I gave it a try. Did it to both a medium & fine tip and needle. I put the fine tip in and sprayed some of the finest lines I've ever sprayed. The best combination I could come up with was 3 parts paint,2 parts thinner @ between 25-30 PSI. The only problem I kept encountering was paint drying on the tip if I let the brush sit for just a little too long (10-15 seconds). Then I would have to open the tip back up to get it to spray again and then close it back down to where I wanted it. I use Model Master Enamels in a Badger 200 single action airbrush. Am I expecting a little too much, or is this something you just have to deal with. I tried adding a little more thinner but then it was too thin to get in close where I wanted to be to spray. I was just experimenting on a junker , so no harm was done.