It sounds like it’s time to take some test shots moving the light around until I figure out what will work in my space. Now I’m starting to understand why
@smoke665 shoots in the dark to better utilize the modeling lights!
UREAKA! He's catching on. LOL Learning proper placement on a human subject was hard for me, even the slightest movement changed things. Then I found the "Other Woman" my DW's Styrofoam wig head. She would sit for hours if I wanted without complaint, and always posed in the exact position I wanted. I set up in a dark studio and worked first with the modeling light of each individual light moving them around and studying where highlights and shadows fell, then turned on all the lights and did the same thing. I didn't fire a shot, instead standing such that my eyes were in the place where the camera would be. That's a key point, it only matters if a highlight or shadow is visible to the camera. Once I had a good idea how placement affected light fall, then I switched to camera to fine tune and study settings for ratios. Now I have a feel for where things need to be so setup goes a lot faster. While you're doing this, now is a good time to study feathering, See how you can use it in your setups.
As to hair, kicker, rim, whatever, location relative to the camera view is the deciding factor. If your unintentional light spill is falling into an area visible to the camera, as in your 1st shot on the cheek, then as I and others have mentioned your light placement is wrong. Notice I used the word "unintentional", I did that because there is a dramatic effect setup that uses side lighting on each side which highlights the sides of the face and shoulders but somewhat casts the front mask in shadow.
@Derrel brought up an important consideration on angle vs specularity. If you're only trying to achieve that narrow band of highlight separation then IMO it doesnt matter, but as you start to move the light such that more of the hair or skin is exposed then yes it matters. I posted one a while back that the subject was solid black, using rim light only to provide a highlight around. Looked like it had been drawn with a white brush on black paper. Specularity is tool, if you use it properly. Also to be considered is the quality of this light as to hard or soft. Do you want a sharp transition on your separation or a more gradual one?
Lastly think about how you use your tools, is it easier to use a chainsaw to cut a tiny twig or pruning shears? The same applies to lighting setups on your son. Look for combinations that provide zones as compared to those that require precision placement at least for now. Just my opinion, but I'd much rather have an image that looks like I placed all my lights correctly with a great expression, then to have something glaring out of place, that takes away from a great expression. As your subjects mature, add to your setups, pick your tools wisely for the application.
