'Relief' comes from the latin word for 'raise' (you can all thank Wikipedia for this), but in actuality, artists don't add to or raise the subject, but rather carve out the background.
At 15 years old, this fascinated me. Sometimes little or no chiseling was done on the actual subject and yet, somehow, a face, a figure or a scene emerged. As the background is dug out of the granite or sandstone or whatever, the characters stand out. They come to life.
I've been working on my synopsis and sent it to a friend who knew nothing of my book, it's premise, characters, etc. I just wanted to see if my synopsis made any sense to her at all. It didn't. She was lost. There was nothing to ground her and nothing that held my string of facts together.
I asked her for suggestions. All she said was "background". She wanted me to carve out the setting. She wanted me to anchor my characters to a place or history. She didn't need much, just something to help her visualize an environment where my characters could come off the page and 'rise up'.
She had a great point. I added only two or three phrases indicating place, time, and circumstance, but that provided enough of a backdrop to support my characters and the series of events in my story.
Often sculptors use 'relief' sculpting because it provides strength and stability - especially at weak points in their sculpture, like the ankles, wrists, or neck. I think carving out a solid background, whether spacial or circumstantial, for our characters will strengthen those weak spots that we may find throughout our manuscripts.
So rather than trying to chisel out the details of our MC's, perhaps sculpting a deeper background might inspire them to rise to the surface all on their own. ???? Good luck fellow artists!