Shadow issue with Skinned Mesh Renderer

[PhoenixOf77]

Hi, i was setting my scene up with SEGI when i realised that i had really strange shadow issues with Ethan (and every other mesh renderer).
The size of the circles you can see on the following gif is changing depending of the Voxel space size. here is the result at 30, the only way to have a descent shadow is having the value between 5 or 7.

Any idea of what coul be this strange shadow and how to avoid it ?

I'm on Unity 2018.1.5f1 btw

https://gfycat.com/LikelyIndelibleGourami