Shadows on a (realistic) small scale objects

Hello I have been looking throught the forums last few minutes and I did read a lot about this problem that we're a lot to have. But solutions that were posted did not work for me. (they were: reduce the shadow distance, in the Project Quality Settings)

The shadows are here, but they are not accurate at all with small assets, like you can see... So here is my scene so you can see the problem by yourself:

Thank you for your help,

Adrien