I ust Tamiya paints about 80% and Model Master the other 20%. I have good luck with the Tamiya paints.
I thin the paint approx. 50/50, using Tamiya thinner. I say approx., because I don't use a specific measuring device. For me, splattering happens when I'm trying to spray with a higher pressure and too close to the model. My AB's have pre-sets for the triggers that allow me to limit the maximum amount of paint coming out. I also turn down the air pressure to 7-10 psi when I'm doing close up work or camo painting. I 've found that this limits splatter. IMO, the closer you get to the model, the more coats of paint you'll have to apply. My first coat on a camo scheme is almost hard to see. However, by the time I've applied the 3rd coat, there is a nice covering of paint.
For general paint application I use a brush with either a .30 mm or .40 mm needle. For close up and detail work, I use either a .15 or .21. I should also state that all of my AB's are gravity feed. I haven't used a siphon feed in quite a long time. A siphon feed will generally require a higher pressure to draw the paint out which could be contributing to your problem.
You state that you use a Paasche #1 (is this the H#1 single?). If so, you're using a single action, external mix brush. the specs list the spray pattern at 1/32 to 1". It needs .5 to 1 cfm, and a psi of 20-45. Here's what I think... With a siphon feed needing that kind of psi, you've got too much pressure when you're near the work piece and splatter is going to happen. When you try to turn the pressure down, due to the siphon feed, you're getting inconsistent paint flow that results in a splattering effect, as the AB need more pressure to pull a proper amout of paint out and to the nozzle. That model of AB is currently sold with a .45 mm needle. Depending on the kind of effects you are aiming for, that could be too big.
While I'm sure there are people using large needle, single action, external mix brushes that get great results. For me, and my skills, it would never happen. I would use such a brush to lay down a base color. For close in detail work, I'd go with a double action, gravity feed, smaller sized needle/nozzle combo.
After all that, I guess I should ask what type of painting you're doing that is resulting in the splattering? If you are having the problem putting down your base color, then have you made sure the brush is completely clean and the needle and nozzle are free of paint build-up? Does your brush have a separate control (at the back of the AB) that allows you to limit paint flow? if so, have you played with that variable? If you are trying to do close up, detail work, then I think you'll have to start using another kind of AB. My memory of the H#1 is that the paint volume control is under a removeable plastic cover on the back half of the brush. Try that, limiting the paint flow - and using more coats - to see if you can minimize the splatter.
Finally, what kind of compressor are you using? Is there an air tank that eliminates pulsing? If not, the paint splatter could be the result of that pulsing. Lots of variables.