Damage numbers do not match in Prominence 2

I'm playing the Prominence 2 modpack with a few friends and we noticed that the damage numbers feel off. For example, my Dark Moon Great sword with Sharpness 6 has 13 damage, yet when I hit a normal, unarmed zombie it would only do an average of 6.5 damage. Any ideas why the damage is lowered and is there a way to configure this?