I presume (with no data in front of me) that if you use the same size ceramic media and propel it at higher velocity (less energy due to less density/mass) then you may get the same peening results (depth of compression) and probably a smoother surface. Another way to get smoother surface is to use larger media size. Small media at high velocity to get the intensity will go deeper into the surface making it rough. Larger media, making the same diameter dent (factor of intensity) will have shallow dent thus smoother surface. Be sure to experiment with steel media and ceramic media to be sure you get the results you are expecting.
