In most of these posts, isn’t the Ambassador just a figurehead, while the Charge d’ Affairs the permanent bureaucrat who really runs the Embassy?
In diplomacy, a chargé d'affaires (French for "charged with (in charge of) matters"), often shortened to simply chargé, is a diplomat - usually a diplomatic Secretary, Counselor or Minister - who heads a diplomatic mission (e.g., an Embassy) in the absence of its titular (e.g., an Ambassador).
A chargé d'affaires represents his or her nation in the country they are accredited to, and enjoy the same privileges and immunities of a regular Ambassador. In most cases, a chargé would only serve as a chargé d'affaires ad interim, heading the diplomatic mission on a temporary basis in the absence of the ambassador. However, in unusual situations, a chargé d'affaires en pied may be appointed for an indefinite period of time. Chargés d'affaires (ministres chargés d'affaires), who were placed by the règlement of the Congress of Vienna in the fourth class of diplomatic agents, are heads of permanent missions accredited to countries to which, for some reason, it is not possible or not desirable to send agents of a higher diplomatic rank (although the countries maintain diplomatic relations).