Paradoxopiped Puzzle

Puzzle description:
The Paradoxopiped Puzzle is a melting block puzzle designed by Gianni A. Sarcone, see https://www.archimedes-lab.org/workshopparadoxopiped.html.
It is presented here with kind permission of the designer.
The box is seemingly filled with nine blocks. But there is an additional block which should be packed into the box. How can you do this?

If you can read German: Mehr Informationen gibt es in https://welt-der-geduldspiele.blogspot.com/search?q=3D-Druck

Puzzle difficulty:
This is a packing puzzle for puzzlers of all ages. If you have not solved other melting block puzzles before, you might be suprised to find out the solution.

Printing instructions:
The blocks fits tightly in the box, so you are not foolished by any gaps. If necessary you can enlarge the box by 1% with your slicer.
The STL file with 10 pieces contains all the pieces you need for the puzzle. An optional STL file for the small piece is provided so you can print the additional piece in