There are currently some issues with reflection accuracy that manifest in certain situations. If you have a Surface Layer in the scene (hard to tell), try going to the Slope Constraints tab and selecting Terrain Normal instead of Final Normal in the lower-right drop-down box. If this helps please do let us know. I've seen it work in a few cases, but I'm unsure how consistent it is.
In any case these kinds of issues will definitely be fixed in the future.
- Oshyan