That is precisely it! Anger and control are inseparable. In a way that also means, that those who are able to get angry have a great sense of responsibility which the utterly detached and therefore calm may have less. The anger however also indicates a need to let go of that which you cannot be held responsible for concretely. One must convert this commitment to others into a more silent and peaceful prayer.
Your insightful words reinforce my trust that we can bear what we are given as long as we don't grasp and cling and take on more than we need to.
Your clients are lucky to have you!