Looks like the rest is on ratios.... the standard in portraiture is 3-1, using a standard main/fill setup. 5-1 is pushing the limit, you tend to lose detail in the shadows. Larger ratios are just split lighting. Less than 2-1 is flat, and pretty boring. The goal with a ratio is to either shape the face or create drama, or both. With a main/fill setup, a 3-1 has one stop difference. The main is hitting the mask of the face, the fill hits everything. So you have one unit of fill, two units of main. Since the fill also hits where the main does, it's 2+1, 3-1.