For now i only have 3 choices of physic objects shape : Cube, Capsule or Sphere.
They do not match my tree log size.
Is it possible to change the shape to cylinder via lua or something else ?
Or is it possible to change the scale with a non-uniform one to match the objet size ?
If you use a capsule you can set the length and radius.
It is rather confusing because you will see a capsule with prototype material on it and you can only uniformly scale this with the Physics Object Scale options. But if you look down the property list you will see you can also set the Radius and Desired Length. Adjusting these you will see a translucent capsule changing size independently of the rendered surface, it is this translucent capsule which defines the collider surface.
So, leave the object scale at 1,1,1. Set the Radius and Desired Length to match the size of your Client Context model. Set the Client Context visibility to Force On and set the Physics Capsule visibility to Force Off. This should enable you to roughly match the radius and length of your log visual.
You can't currently join physics objects to make more complex shapes.