After more investigation I think we found the issue...
First I was thinking (like Elizabeth and Phil) that it must be an aspect ratio thing. But we checked and, although my resolution is higher than the client's, our aspect ratio was the same (16:9, or "widescreen"). We both have the same aspect ratio and yet we're seeing different size content.
But as we were discussing, she mentioned her eyesight, and I asked if she had her display scale / zoom setting bumped up. She said yes, she always has the zoom increased on her display to make things larger and easier to read.
I increased the zoom on my display to 150% and, sure enough, the Storyline content shrunk. Whether by design or by accident, Storyline shrinks the content area when Display zoom is increased. The Player gets bigger, but the content area gets smaller.
Going forward, given the prevalence of high-def displays today, we will factor this phenomenon into our design decisions.
- Hi-res monitors leads to smaller onscreen text
- which leads to some users increasing their display scale
- which leads to Storyline content area shrinking
Hope this is helpful (and not just being Master of the Obvious :) )