It's the "unit within a unit" for me too, though it does depend on the specifics of the characters and situation. One thing I think is kind of funny is that it took a long time for me to realize that this is not just a thing for me, but THE big thing. I think it took so long because I'd always noticed the individual character relationship(s) and that was what I kept looking for, characters who could give me those feels, but I started getting WAY better at guessing what was going to hit me in a fandom-type way once I started noticing how much the ensemble mattered. I used to think of it as "a character relationship I was into, plus a fascinating world I wanted to read/write more about" but eventually I started to realize (especially once I started getting into non-SFF fandoms where the worldbuilding clearly wasn't the big draw) that the "world" part was really more the group of characters surrounding whichever of the protagonists I was specifically into. A group of people who are all kind of "weird" about each other and loyal to each other, even if (especially if!) they don't always get along, and especially if there's also a domestic living-together element to it ... that's really what most of my fandoms, and most of my favorite canons, have in common.

Though as far as individual relationships go, that thing you're talking about where the character who's nominally in charge in the hierarchy is not actually the one who's in charge in their dynamic is also something I really love, and it is definitely an aspect to why I like the Peggy/Daniel/Jack triad so much. Especially when they both outrank her, but both just do what she tells them anyway. :D (But it's sort of like ... I think a part of what makes it work for me is that the characters themselves do actually still follow the hierarchy "rules" anyway, they just subvert it at the same time. Peter and Neal were like that too. It's not that Neal ended up asserting himself as the dominant partner in particular; he didn't want to. But he didn't just take orders either.)