You need to edit this image:

Since it has those triangle at the bottom, your preset will not have that blocky look to it. It's located in your textures folder and it's called fmaneShadeSpiked.
If you're using GIMP you can use the "lock" tool on the layers menu so you don't go outside the transparent lines.If you plan on using layers you can make a new layer and change it to Multiply or Overlay so you do not go outside the lines.