Pixelated dark regions in rendered shot

Hi Folks,


In the above snip from the rendered shot you can see that the dark regions are pretty pixelated between greys and black. The scene is lit only by a sky sphere(from engine content), exp fog and a spotlight. Im rendering exr at 2K res with 16 temporal samples.
Any suggestions to fix so that the light and dark regions have a gradual transition?
Thanks in advance!