Specially this: > In general, it's Block or Dodge but in certain circumstances a GM might allow both. However, you still don't get to add the two together.
But the books examples about rolling defense within a block. But it's not clear if the defense must be against only the shifts that surpass the block it the full attack roll
For example, a 2-4 shifts could simple add some Aspects on the scene, with free invocations for the enemies. Anything beyond that could easily hit everyone in the area with 4+ Shifts. Huge backslashes (possibly caused by Thaumaturgy) could make things really interesting, like summoning/setting free a demon or throwing the PCs to anywhere in Nevernever.
@doppelgreener @doppelgreener I still have to get my hands on The Paranet Papers. As I read about it add some updates to DFRPG systems. Probably based on FATE Core.