That's because the spit attack (from the tutorials) just spawns the prefab via it's damage dealer doing damage - this spawns the prefab where it hit something.
For more complex things, use a schematic to animate the damage dealer's hit - here you can spawn a prefab on the ground by e.g. first finding the ground position via a raycast (at the hit's position.
However, the best way to handle this kind of thing is to have the particle effect itself handle that. E.g. Unity's visual effects graph can create awesome and complex effects like that :)
