How to design a fundamental single-key setup for versatile, flattering headshots?

[Ronald77]

I'm a portrait photographer transitioning from natural light to mastering studio lighting, and I'm struggling specifically with portrait lighting techniques for creating soft, dimensional light that flatters a variety of face shapes without looking flat or creating unflattering shadows under the eyes and chin, especially when working with a single key light and modifiers. I have a basic two-light setup with softboxes and a reflector, but my results are inconsistent, and I find it difficult to pre-visualize how moving the light a few inches will change the mood and shape of the face. For studio portrait specialists, could you share your foundational setup for a classic, versatile headshot? How do you determine the optimal key light height and distance relative to the subject, and what are your go-to modifiers and fill strategies for achieving that polished yet natural look clients expect for professional branding sessions?