Humbrol acrylic thinning issue?

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..

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? 

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.

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.