There are a few settings you have to leverge. Reducing bias will keep particles more towards the center of a given cluster. Also you can use Object Bind in surface bind mode (with snap on) to constrain particles to a surface.
If you want a closer idea of how the growth algorithm works, to better understand the results you're getting, look up diffusion-limited aggregation.
If you want a closer idea of how the growth algorithm works, to better understand the results you're getting, look up diffusion-limited aggregation.