I have 27 artifacts in a set called "Daze". Some are rare and some are epic. Some are 3*, some are 4* and some are 5*. They all say the same thing above the Upgrade button

"4 artifacts per set

25% chance of placing sleep debuff” 

So that means the set Daze has subsets with 4 artifacts in each subset, right? How do I tell which artiacts are part of the same subset? I need all 4 from 1 subset to get the 25% chance of placing the debuff.. Would the artifacts from 1 subset always have the same rarity and rank? I've got rare 3* helmet, shield, gloves, chest and boots. That's 5 artifacts. One doesn't belong. I might have 1 or 2 complete subsets and the rest are incomplete or I might not have any complete subsets. How do I tell which artiacts are part of the same subset?