http://docs.unity3d.com/Manual/UsingReflectionProbes.html
Blending section mentions "When one probe involved in the blend has a higher Importance value than another, the more important probe overrides the other in the usual way.", but it doesn't happen

To reproduce:
1. Open attached project
2. Open scene 1
3. Increase importance of one of the reflection probes
4. Notice that the sphere between them, still uses both equally

By design:
Reflection probe boundaries weren't overlapping