why the magnification produced by a concave lens is always less than 1?

the magnificent of  image formed by concave lens  is always less than  1.a concave lens is thinner in the middle and thicker at the edges. a concave lens is also a diverging lens. a concave lens will make an image that is always virtual, upright ,smaller than the object. the magnificent of a lese can be calculated by the below formula

magnificent=image height/object height