Hmmm, it seems you have dropped the image. So going on memory (not the best choice, I must say) your image was about lighting.... side lighting with the opposite side melting into the darkness. This is slightly different from
Rembrandt lighting which includes some detail for the opposite side of the main light source.
Just to have a little play, I tried to emulate your objective. First off, I decided that I wanted to shoot at f/9. This is the metered shot at f/9.... ISO200, SS - 1.3" to get a "zeroed" meter reading. (Still slightly underexposed to my eyes).
As you can see, I have the subject backlit with a diffused window to camera right.
Initially, for some reason, I wanted to shoot an f/3.2 aperture, but it turned out to let more ambient light than I desired (the left ear).
I tightened in the zoom from 62mm to 70mm, stopped down the lens to f/9 and adjusted the flash power to ~1/32th.
Thinking that might not be enough to pull out all the detail I wanted, I upped the flash power to ~1/16th power.
Those two images gave me a range that I could play with. BTW, I used an 8" snoot on an SB600 to light the subject. IgsEMT thinks they're only suitable for specialty lighting, but I tend to disagree. Snoots and grids are perfect for when you want to highlight a particular spot in the scene. Some times there is a specific detail you want to highlight....., (one of ...) the only ways is to hit it with controlled directional lighting.