I have identified the nether creatures that appear with a major and minor sigils because I had a doubt about their levels.
I was in a level 25 realm when I have used the sigils. The minor nether creature was level 373 and the major one was 338. I was expecting that the major one would be higher than the minor.
I don’t know if it is working as intended but I’ve always had the feeling that minor sigils were harder than major sigils.