The more power you have, the less honest some feedback becomes automatically.

The distortion is automatic and it is not about the honesty of the people around you. Consequences change what is easy to say, so information reaching a powerful person is softened, delayed, and edited by ordinary people acting reasonably. You do not have to do anything wrong for this to happen.

Assume it is happening rather than hoping it is not. Go to the source occasionally, ask specific rather than general questions, and pay attention to what people tell you when they are leaving.