It's hard to tell what your perceived problem is from the pics. I'd start by not using water as a thinner. It does work, but it's one of the least effective thinners.
You could use the proprietary X-20A acrylic thinner, Isopropyl alcohol, denatured alcohol or, when you get a little more advanced. lacquer thinner.
My next suggestion, assuming that you use one of the alternative thinners I've mentioned, is to thin the paint more and perhaps reduce your air pressure, depending on your airbrush setup. Tamiya acrylics work best when very thin and at lower pressure (and correspondingly, at a close distance to the subject).
When airbrushing with acrylics, particularly Tamiya and Gunze, you should not exceed about 4-6 inches distance from your airbrush to the surface that you're painting. If you do so, you will run the risk of "pebbling", which is the paint drying in mid-air before it reaches the subject, causing a dusty, grainy finish.
The key points are:
- thin paint
- low pressure
- short distance to subject