Should be able to place a block on top of a hopper while aiming at the top of the hopper and shift clicking with a block in your hand.
- The block cannot be placed. If far enough away, or if the block has no collision (like a rail), it is placed in front of the hopper.
- Aiming at any of the side faces of the inside is like aming at the outter side faces.
- If aiming at the bottom inside center or the outer top edge of the hopper, the block can be placed.