This is likely because your Camera node uses a different Far distance. If you leave the DirectionalLight shadow max distance to 0, it will use the camera Far distance to determine the shadow maximum distance. (The higher the distance, the lower the shadow quality will be.)
To solve this, decrease your Camera node's Far property or set the DirectionalLight shadow max distance property to a non-zero value.
PS: Sharper shadows aren't always better. Shadows that are too sharp can end up looking very artificial :)