I've included an image of his work with 4 shading strategies I quickly mocked up. If any of these seem closer to your vision it may help guide us on what to change.
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A represents standard engraving where the lines follow the depth of the drawing and line thickness determines how dark the shading is and the line density how steep the edge is (like a normal height map).
B represents the kind of engraving you'd see on money where lines are very fine and follow the depth but are interrupted more often in lighter areas. This also works the same as A.
C is a refinement of the straight lines used by the artist above where the lines are worked into some of the line work but follow the curves of the drawing, in this case his pectoral muscle.
D is crosshatching but I suck at it and did a bad job on the mockup. Basically this is one of the more basic techniques taught in high schools but does make for good results when done with more patience
Many of these can be combined, like A and B. A and B can also be done in a cross-hatch style (as seen on the $100) where they used round tip AND sharp tip gravers! This is probably the HEIGHT of engraving accomplishment, can't get much better than that.