Humbrol acrylic thinning issue?

I have now tried the Humbrol acrylic with Tamiya thinners in ratios from 3-2 to 1-1 & I still have the same problem. I did find things slightly more workable by bumping my compressor output to 30psi (which is twice what I usualy use in my gravity brush with Tamiya). The paint looks clean & consistent & is pretty new.

Help, I'm stumped. 

Could it be possible that the paint is still not thin enough to cycle thru the AB? I think that if you needed to increase ap then the paint may still be a bit thick.

When I tried the stuff at 50/50 with Tamiya thinners or water, the paint gave very poor coverage - you know when it gets that thin you can almost see the pigment floating around in the carrier when it lands? I had assumed at that point adding any further thinner would just cause more problems & result in umpteen coats being needed.

Have you used Humbrol Acrylics? 

I've haven't used their acrylics but I've used their enamels in the small tin cans for years and they are my favorite enamels, specially for brushing. I have used the Tamiya, Polly Scale  and MM Acryl paints without  any problems. I cut them with either alcohol or distilled water with a drop dishwashing liquid soap, but they have to be extra thinned for airbrush use, otherwise I get a lot of spitting and grainy texture..