hi jeremy,
the best thinner to use, although expensive, is mr. gunze thinner. i dont have an exact ratio but when using tamiya sprayworks, i add paint to the thinner until it has the consistency of milk (not evaporated . :-)). use a thinner consistency when painting camouflage patterns.
you can use hardware lacquer thinner or automotive acrylic thinners. but be careful as these melt plastic. airbrushing a thick coat of paint at one pass may 'craze' the plastic.
you can also us hardware lacquer flo. this does not melt plastic, but may dry a bit slower than gunze thinner. or you can mix both laquer thinner and flo.
if i may suggest further, to conserve mr. gunze thinner, maybe you can use mr. gunze thinner only when painting the exterior of the model including the clear topcoat and hardware lacquer on interiors like cockpit, wheel wells, cowling interiors including engines, landing gears, etc.
with regards to your problem on 'webbing', your paint mixture is just as you said, 'sobrang lapot' (too thick). add more thinner until your mixture has the consistency of milk.
hope this helps!
bigman