Between the fine folks at Mission Model Paints (they answered all my concerns) and an article from Model Paint Solutions (John Miller), I now have my MMP paints spraying great without the dreaded tip dry which plagued me before.
I'm using the method prescribed by Model Paint Solutions to thin MMP paints using a 10:1 MMP thinner to MMP Poly mixture. With this 10:1 mix, I thin MMP paints as follows:
For base coats - 60/40 (paint to thinner/Poly mix) (spray 15-18 psi)
(for example: 6 drops MMP paint and 4 drops thinner/Poly mix)
Camo and fine lines - 50/50 (paint to thinner/Poly mix) (spray 10 psi)
...it took much effort but this works for me.