I also stopped measuring thinning ratios and go by feel alone. Here is what you can do to find the sweet spot. If you find that your paint is too thick, you can add thinner one or two drops at a time and retest. Repeat until you get a satisfactory result. If your paint is too thin, add more paint and retest. By the way, I always used Testors "universal" acrylic thinner to thin their paints.
This is a bit tedious at first, but after a few times you will learn the right consistency.