Pretty straightforward. In the rulebook it seems a force 6 spirit will typically have a reaction of 12, 18 or 24. Making it one dodgier than most munchkins. Was this ever erratad or somesuch, or is it just another way that spirits are supposed to be extremly hard to deal with unless you use magic? (Which is how I've been playing it).

how old is your copy of the rulebook? i'm pretty sure that made it into the very first errata... or maybe it was known and addressed before the first errata, and then not incorporated for some unknown reason...

either way, it's been reaction based on force + some number for quite some time now, and is no longer force x some number.