This isn't yet public on the main site, but you can access it via the direct link below:
Portrait Lighting, Part 2: Adding a Fill Light
This article covers the influence of the fill light ratio and fill light placement, amongst other topics. If you haven't seen it already, also see the background article entitled introduction to portrait lighting (with one light source).
As usual, please let me know if you feel anything is unclear, if you notice any typos, or just want to add something from your own experience.
I'm still debating whether to give reflectors a more thorough treatment, or to make that the focus of a separate article later on (so that part may change).
Many thanks!