I made Avan Geiserford with less defined abs because I don't really like characters with exaggerated abs or a bulky build. If you want the lean muscle look to stay consistent, you can add "lean body" to your prompt. If you want the body to look smaller, try adding "young man" or "youthful" even "shota".
I’ve also tried generating some R18+ images on Civitai, and the results were fairly decent—though of course not as good as the original visual.