A little language problem
A little language problem here. “Snap” does not really describe to me what you want – sharp edges, brilliant colour, etc.? “flow” also gives me a difficulty. Is this how it comes off the brush, how it lays on the glass, etc.?
More helpfully, you can look on YouTube for glass painting tutorials. Peter McGrain has a video too. these can help both in consistency of the paint before applying. (With no tooth, I would assume the paint would flow better than on, say, paper). If you have a medium, you should not need gum arabic, which helps paint flow off the brush more easily.
The temperature at which you fire the paint can also have an effect on the brilliance of the colour. Firing too high pales the colour. Of course with enamels you will never get the intensity of colour that glass gives.
You can increase the intensity of colour by repeated applications.
Also, it occurs to me that you may be using opaque colours rather than transparent. The transparent allows more light through and colours the light rather than blocking and reflecting the light that opaques do.