Heya, first I think you may get a slightly different result if you use the spray alpha with some various brightness (there should be one in by default). That would make your spraying less uniform in depth. Also there's a setting if you right click the actual brush. I can't check atm and I just don't remember what it's called but it's a way to lower the intensity influence on the brush, by default I think it's 4-5 on a lot of brushes, you could try lowering that.
But I don't really think you're that far off, it's a lot about brushing the whole surface really roughly first, then perhaps use an inverted brush and go over the whole thing again. Sometimes it looks really horrible until you've gone over it enough.
Hope any of that made any sense