Hey akaChrisV,
We are aware of the limitations you have pointed out in your post, and we have quite a few reports in to fix and improve the reflection capture actors. Getting something to be physically accurate is not completely dependent on reflections, as the material editor is where you create the PBR material so it renders accurately under any number of lighting situations.
Our Senior Graphics Programmer provided a very in depth explanation of shading within our engine. We also have a number of other resources which you can also explore.
Real Shading in Unreal Engine
Resources
Let me know if you have further questions or need additional assistance.
Thank you,