I’ve already stipulated to that more than once. And I’ve also already said more than once that it is the least common form of polyamory. Closed relationships of one man and two or more women (or two men and one woman) who only have relationships with each other is so rare as to not be a factor in harems beginning to emerge as a widespread societal construct. In most cases, that’s actually polygamy and not polyamory anyhow due to the patriarchal power dynamics, which are notably absent in actual polyamory.
In this story about my personal relationships, which I’ve already linked to you, there are descriptions of some of the most common types of polycules.
I am in both a V and a triangle. Even though I have two men whom I consider to be life partners, I still have other meaningful and casual relationships as well. This is much more common in polyamory than closed relationships.