Thanks Kelly, turning the air cap 1/4 turn will give you as much information on gun set up, as having the pattern up and down...a flat pattern will tell you exactly where the problem is by watching the runs, if your thick in the middle, you need more air or less fluid, if your thick on the ends, more fluid or less air...for fine tuning, this is a valuable technique for gun adjustment.
By doing this, especially on those pesky light colored metallic's, your taking another part of the tiger stripping problem out of the equation.
I sincerely suggest this method for gun set up, many people just listen and after a while know their equipment, assume that everything is clean, when we have all had experience with that little piece of dried whatever stuck in your gun causing a problem with the way the gun sprays or when you run into that color where no matter what you do, the color stripes..this procedure can most times solve that problem when understanding what happens to a spray pattern under different conditions.
I really hope that this will help, for me it was a little thing I do religiously, 95 times out of 100, the pattern is fine...for the 5 times out of 100, it helps analyze the problem much quicker when you understand how different things effect pattern, both horizontally and vertically...just another piece of information I'm happy to pass on.
All the best.