sometimes when lighting a face for an interview, the highlight reflections off the face seem almost blown out, but adjusting the exposure or moving the light back doesn't seem to help. I've assumed that some people just have more reflective skin than others?

Now I'm wondering if the diffusion on the light isn't wide enough to soften it enough to spread out that reflection?

any suggestions?

Keep some oil control powder in your camera bag and some of the little oil blotter papers too. Work wonders on shiny spots.

A field monitor with False Colors gives you a realtime readout on exposure. It tells you exactly what the IRE is on each reflection. Using it will make what's going on more obvious. Sounds like you are dealing with the dynamic range of your camera. That is, for some faces, if you dial down the exposure because of the highlights, the rest is underexposed? THere may be other color profiles and gamma settings that could help. What camera are you using? You mentioned a soft light source. What are you using for that?