Instead of decreasing/increasing attack distance, it decreases/increases block breaking distance.

I'm assuming 1.14.4 since you gave no information. Please follow the template next time.

I'll probably have to ask Forge about this. They're the ones who add the reach distance modifier.

I confirm this, spears reach is only increased for blocks, but not for entities.
Using
SilentGear-1.14.4-1.4.6+72.jar
SilentLib-1.14.4-4.4.0+44
1.14.4-forge-28.2.0

Fixed by c592ede and 6dcaebe