As odd as this might sound, it could be a problem NOT thinning it.
I found when I shot Future full strength that it was a bit of a pain in the backside to get right. You need it thinned with some alcohol to makeit dry a bit quicker, and also to level out better. That's what works for me.
Incidentally, I find that if I take a jar and make 1/3 Future and 2/3 Alcohol, it makes dandy thinner for any brand of acrylic paint, including Tamiya. The Future re-inforces the paint, making it dry harder and shinier, and more sandable.
If, by chance (like on my current project, the Hertz SVO) you end up with a colour that's flat, thin it down with Straight Future a bit, then airbrush it. Unless you thin the paint until it doesn't cover, you can ALMOST NEVER add too much for airbrushing purposes. Handbrushing is different, of course!
Good luck! I'll be interested to see how it goes!