You would need to check where the edge of the displacement map is on the figure.

 If you are using a setting which represents no displacement as black, with a map which is designed for no displacement at mid grey, then you will get a step at the edge of your displacement map because the whole area of the model covered by the map is being displaced 50%. In the middle of the map, such as the forehead, it will look 'right' beause you have zero displacement/50% displacerment/ full displacement.