Another way to shade a region in 3 Proportions would be to draw strains on top of each other. This way you maximize the level of black and therefore produce a shadow. A while ago, I chose to follow my sketching by drawing in my sketchbook every single day. https://inkpendrawingtechniques81369.total-blog.com/ink-drawing-for-beginners-can-be-fun-for-anyone-62598513