Objects' shadows are not clear in the terrain

Hi all,

We tried to bake the lightmaps for our new game since we target mobile platforms.
The map uses a 500x500 terrain. We follow the setting as we did before but the shadows of the object casting on the terrain are not clear. They are very blurry.
Then we increase the setting as you can see in the attachments but it doesn't help much. The shadow is a little bit darker but still blurry.
You can see the baked lightmaps here: https://www.dropbox.com/s/ensme59jpyu98m2/Map Island.zip?dl=0