You don't get it. You have to move the center of mass, not the collision shape itself. So the shape has to move up when you move its center down... The center of a collision shape is always its center of mass.
To create a collision shape with its center of mass outside of its volume:
- Create a node "A" at 0/0/0
- Attach a box "B" at local translation 10/0/0
- Make a collision shape from node "A".
- Now note how the collision shape looks like a box at 10/0/0 but its center of mass is at 0/0/0
This is because of what was said repeatedly now - the collision shape always has its center of mass at its origin. The collision shape was generated from the node at 0/0/0, so thats its origin. The volume or mesh of the collision shape was at 10/0/0 though, so thats where you see it and bump into it.