Some tracks move sand toward the outer edge, some toward the middle, and some are “neutral” in this regard. After running a playlist repeatedly, you may notice a net movement in or out (more often outward). If you want more sand in the middle, you can run the playlist called “plow in” repeatedly (overnight is a good time). If this playlist is not already included on your app, you can create it easily: Go to “Playlists”; hit the ‘+’ button; change the “New Playlist” name to “plow in” or whatever name you want; then add these two tracks: “e10” first and then “apache1”. It is important that you do it in this order, and that the tracks play in order – NOT shuffled – and be sure to save the newly created playlist.