We would usually talk about intimate network for the whole relationship (with all the people involved, no matter the size) and then different terms for different sides.
Or you could phrase it from the point of view of a single person ("I never thought of a mono being in a relationship with a poly" or "I never thought of a poly being in a relationship with one or more mono(s)")
It's true that I too did a double take when I read "couple". It is basing it on the idea that these two people are the "real" relationship, and that other people would be extra or additional. Even if these two dated before adding other people to the relationship, there is no saying people in the relationship see it that way (a couple plus others) rather than seeing the relationship as a whole. And the mono partner might be a partner who joined the relationship later, too, and then excluding other, more established partners might make even less sense (why are these two the "couple" when their relationship is three months old and others are twenty years old?).
But we're teasing you, really. Just trying to give you a different perspective here