Abrasive media (for deburring, radiusing, blending machining marks, etc…) needs to have an ‘open face‘ to work as it should. This is where you can feel the abrasive particles when dragging your finger nail over the surface of the media (like a file).
As most media (ceramic and/or plastic) wear, the level in your machine can drop significantly over time. As mass finishing processes work by covering the part with the media and the media moving over the edges to create the deburring, radiusing, etc.. it is important a ratio of media : parts is retained.