Convex Mesh Collider not matching Convex mesh's shape

When using mesh colider (Convex) it does not match the shape, I know that turning off convex works but the shape is a rectange,

It’s hard to tell from your screenshot. However a convex mesh can’t be a rectangle since it needs to have “depth”. A convex mesh collider represents a closed convex volume. That’s the point of having a convex mesh collider.

Regardless of the original mesh, Unity will always calculate a new convex hull for the provided mesh. So vertices will never match.

thanks for your input however i found that adding more geometry to the mesh solves the problem