John, that sounds fine to me. If the paint is flowing properly through your airbrush, and you are getting the coverage that you want then that's what counts.
The actual ratio depends on type of paint, type of airbrush, and how you paint. For example, if the paint has been left open in the bottle, you might have to thin it a little more than normal because some of the solvent will have evaporated making it a little thicker. Some metallic paints are pretty thick and others are pretty thin right from the bottle so you might have to adjust some in cases like that. How well it paints is more important than the actual ratio of paint to thinner.