Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - General Dagger crafting - WHY??

I craft a level 15 dagger.

At 3 Blacksmithing, it does 63-106 damage.

At 4 Blacksmithing, it does 60-100 damage, and all other stats are the same.

At 5 Blacksmithing, it does 60-100 damage, and it has 10 more durability and some kind of stat boost.

Why does the damage go down? Why is it worse in every way to craft it at 4 Blacksmithing instead of 3 Blacksmithing??