First cast ever. Did not know how hard this can be. This required my constant thinking.
First I made a mistake by putting in shadow value too early, before I have a proper shadow line established. Erased that.
reestablished the shadow line. Then put back in a single value in the shadow. (below)
I put in the back ground to the darkest, which is called Keying. Then I go around comparing the relation between values next to each other to their relation with the background value and lighten/ darken accordingly.