Auto painting with watercolor brushes

I have been working recently mostly with watercolor brushes. I've been playing around with using auto painting to lay down an initial wash or underpainting layer, mostly as a way to get a head start for a quick painting, but it's not really working out the way I need it to. If I use the watercolor brushes in Smart Strokes category, the results are blotchy and just generally unattractive. But using other watercolor brushes it almost doesn't work at all. The same if not true for oils. I can pick pretty much any oil brush, set the opacity low, start auto painting and and get a nice underpainting effect in a minute or so.

Has anyone else worked successfully with regular watercolor brushes (not smart strokes) and auto painting? Would appreciate any help or tips.