Unity 5: Raycast on non-convex Mesh Collider

Question

I'm using this code to raycast on objects and fire events:

if (Input.touchCount == 1 && Input.GetTouch(0).phase == TouchPhase.Began)
{
    var ray = Camera.main.ScreenPointToRay(Input.GetTouch(0).position);
    RaycastHit hit;

    if (Physics.Raycast(ray, out hit, 20))
    {
        var evt = hit.collider.gameObject.GetComponent<GameEvent>();

        if (evt)
        {
            EventManager.RegisterEvent(evt);
            return;
        }
    }
}

But it works only on those objects with convex mesh collider. If I uncheck the convex checkbox on the mesh collider component the script stop working on that specific object.

Is there something I'm missing?