If we look at a convex mirror diagram, it produces a real inverted image at the bottom. Let's say a person's eye is above the object. How do the reflected rays reach the eye? since it's a concave mirror, the rays are being reflected toward the center which would be away from the eyes, right?
Try drawing a ray from the top of the object through the center of curvature (C) which hits the mirror radically and will be reflected right back on itself. This gives you an example of a ray that you could see if the eye was above the principal axis.