You are doing VERY well for just starting to try portraiture with one light! "Rome wasn't lighted in a day."
Learning lighting from diagrams in books or from the web/net can be a bit tricky; there are a number of difficult to define variations that can significantly alter how a set-up needs to be positioned. Different beam-spreads, different modifiers, different grids, different everything.
If you look at on-line lighting diagrams, MANY of them will show reflector positions that are way too far behind the subject's face; placements that will illuminate the shadow-side shoulder and shadow-side ear in an unflattering way, and which will also illuminate the nose to a weird degree. A basic rule of thumb is that the reflector needs to be in front of the sitter's placement!
On the internet one will encounter many lighting diagrams that will show incorrect or useless lighting placements, placements that just simply do NOT work...stuff often drawn up after the fact, from memory, or worse, drawn by illustrators for authors, or drawn by computer software programs by people who really do not fully understand actual, best practices, or nuance. You'll typically see references to this issue only from observant, master-level lighting instructors.
Different lights can and do cast different beam spreads; flood lights can easily have 65 degree beam spreads,all the way up to 110 degree beams, so it's possible to get a catchlight from a 110-degree beam spread light that's wayyyyyy off-axis! If it's a BRIGHT light, say a 250-Watt quartz lamp, the eyes will have brilliant catchlights.
You are undertaking something that is not especially easy to do without an on-site mentor to show you some of the nuances. In the solo shot of your granddaughter in Post #15, the light is positioned at a good height to give a 1 o'clock catchlight, but in the dual shot, her head is turned down, and her eyes do not reflect the light; it's a near-miss for her, but fine for the boy. This is why in the other thread, me and AKUK are stating that a speedlight is not the ideal tool for learning how to light...you just do not have the visual feedback to literally see what the light is doing, as people move, pose, and re-pose, and so on.
