According to IIA guidance, the practice by the chief audit executive (CAE) that best enhances the organizational independence of the internal audit activity is meeting privately with the board at least annually.
This practice ensures that the internal audit activity can operate independently of management and directly report and discuss significant matters with the board, which is critical for maintaining its independence and objectivity.References: The Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing.

The board of directors plays a leading role in overseeing the ethical atmosphere of an organization. They are responsible for establishing and promoting the organization's values and ethical standards. The board sets the tone at the top and ensures that senior management implements policies and procedures that support ethical behavior throughout the organization. This oversight includes monitoring compliance with ethical standards and addressing any ethical issues that arise.References:
* The IIA's International Professional Practices Framework (IPPF) - Practice Guide on Ethical Leadership.
* COSO's Enterprise Risk Management - Integrating with Strategy and Performance.