Hi all and thank you for your response.
I must admit that I'm lazy, that's why I use PlatformBehavior, but with the worries that implies I give up this idea.
With Ashley's explanations I realize it's not a good solution to base a simple game as Tetris on a complex system.
I realize that making a stepped movement way is a better solution, a better start.
Starting from scratch sometimes saves time ... I just lost more time trying to make the PlatformBehaviours set up my ideas than I will have wasted trying from scratch.
Anyways, I'll post the final solution here, as it benefits everyone, although Yann gives me the solution on a plate!