Alison said:
...I'm wondering if using a reflector on the other side would be enough and if not where I should be the second strobe.
I subscribe to the old rule that it's best to create lighting that appears to come from a single source. Now, remember... photography is essentially recording reflected light. So if there is no light on the shadow areas of the portait (or on the background), there will be no record. With this in mind, a second light should be positioned so that it is not evident, creating light that is as shadowless (flat) as possible.
It's at the makers discretion just how much detail to record in the shadow areas. This is reffered to as lighting ratio, since it speaks of how the MAIN light (also called the KEY light or MODELING light) relates to the FILL light.
Since I always use a lens with a focal legnth that is about "twice normal" for portraits, I can get the MAIN light (sofbox) in pretty close, preserving the quality of light and creating large catch lights in the eyes. Two things happen when you move the light farther from the subject; The catch lights will be smaller, but perhaps more important, the light becomes more "directional", increasing the need for a second light to preserve detail in the shadows.
So when making portraits of individuals or couples, using a longer lens, it's possible to keep the sofbox and reflector in close without coming into view. When photographing groups, it becomes necessary to pull back the camera and lighting. So in this case, I use a larger sofbox and a fill light with umbrella.
This is a basic description of portrait lighting. There are other subtleties that one must address, like detail in the hair and separation from the background... all like adding spice to soup. If one choses to use additional lights to address these issues, they (generally speaking) should merely add to the "flavor" of the portrait and not dominate on thier own.
Or course, some folks don't like garlic. What I mean is the photographer's use lighting defines his or her style of work.
I hope this is helpful. It's difficult for me to relate this in writing. I wish I could just show you.
-Pete