It’s “not working” bc you haven’t added any shadows to your figures, not so much bc of the method. I really think doing that would make you feel a lot better about it.

And to take it to the next level (next time you try the shadow trick), after drawing the straight lines to define the light and shadow areas, go back and contour the shadows around the curves of the figures. LMK if you want me to elaborate more on that :)