Finally got Ammo by MiG paints to behave for fine lines and mottling using Mr Color Leveling Thinner, 2:1 Thinner to paint. They lay down nice fine lines and mottling. I do recognize that thinned this way they're now out of the water base category...
There is a alcohol component in Ammo thinner as Tamiya has with theirs. We all know how well Tamiya sprays with Mr Leveling Thinner. Mr Leveling Thinner also works great with Ammo acrylics, at least for me. I also lay down clear coats on all my paint jobs to seal for decals and subsequent weathering steps.
Thinning Ammo paints with Mr Leveling Thinner is working for me and I like Ammo's selection of colors and their artistic rendering for Scale effect. Regardless, weathering brings them into the right shades for scale proportion. YMMV.