I haven't rounded the corners on my stones, so I can't really help there.

For the changes in surface consistancy, you could try using a new piece of sandpaper (assuming you are using sandpaper on a granite tile) for a couple of strokes. I find that sometimes my sandpaper gets a little worn out and the effective grit is higher than stated, giving a smoother finish than I am looking for. I like a 120 grit finish on my 4k stone.