Hey Ed,
The Aztek is a victim of expectations greater than ability I fear. I've fought that fight in the paint forum and in most cases I think what happens is people expect the Aztek to do something it is either capable of doing, they set their own expectation higher than their ability, or as a result of failed expectation blame the airbrush. Very few practice or experiment they just fill, point and shoot. If you look back through the archives you'll see almost as many derogatory comments on lost time, difficult handling and prblems with brushed like pasche, thayer chandler and iwata.
Not to say Aztek doesn't have its shortcommings, but if you don't expect it to do more than it is capable of, you won't be disapointed. I think alot of people are turned off by its light weight. But I digress.
I use pretty much the same set up you use. The tan tip for most of my work. By adjusting the flow (the roller in the back) you can really get some nice paint control. For really fine work, I use the black tip. I also add a few drops of acrylic airbrush medium which seems to keep it running smooth. A quick clean between cups and I'm ready to go. I also keep a "sacrificial board" near my paint set-up when I shoot. This allows me to make sure everything is flowing properly, and make any fine or tight adjustments necessary before I shift to the model. I always make a couple of passes just to make sure before I lay down some paint on the model.
The 3:1 or 4:1 mix is pretty good for dark colors and I use a 2:1 or 1:1 for light colors. (less particulate in the paint) On really fine work, I get real close to the object. And knock down the pressure a little, between 15-20 psi.
Don't try to do it all in one pass. You aren't doing illustration work so the paint you are using is heavier. It will stay sharper and you will be much happier if you make a couple of passes when you do fine work. (This may be where alot of guys go wrong and expect the airbrush to do too much) Since this is acrylic paint on primered plastic it will have different application characteristics than guache on illustration board. Thus what may be accomplished in one pass when doing illustration work may take a few passes on the model. Patience. Practice and Patience. Spend a day playing with the Aztek and trying stuff out. Every combination etc. to see what offers the best results. Different lines, the way you hold it, is it perpendiuclar or are you shooting at an angle, different tips, pressure combinations. I also use a bird feeding syringe (available at pet stores) for measuring paint going in the cup. This gives me consistent results and I keep a little notebook of paint color formulas, additives, and thinning ratios.
It is a very capable brush and works well on most everything. I had thought about picking up an Iwata just to try something different but the more I think about it the time I would lose in cleeaning, tuning, repairing and or waiting for parts etc. I could better spend my time building. Although that new metal body Aztek has definately caught my attention.
As I was doing this project I seriously thought about the Leopard and Panther that has been mentioned. Just for a change of pace but I think more importantly others are willing to try something like this. Too often we get carried away with matching exact colors, amount of detail and variant configurations with what particular markings that I think detracts from the overall experience. As Robert said, this was sort of inspired by a few of the rivet counting threads and the purist vs. the leisure builder. Mind you I will count some serious rivets and I appreciate those guys alot. Because of them we have a wonderful aftermarket to choose from and the quality of kits has gone up. I am guilty of wanting to look at my kits or builds and wanting the exact copy of the 1:1 vehicle. If it existed on the real thing I want it on my model, but I also think that it can be balanced with personal enjoyment and frivality that makes this a fun hobby.
Now excuse me, time to look under the bed and in the closet, I think Whitmann's ghost is prowling around looking for the defiler of Tigers.
Thanks for the compliments,
Mike