This is great @Audz! I’ve always thought that picturing the relationship as an arc or “graph” is a great way to understand it better. I hadn’t considered that certain shapes of that arc might be more common and thus considered tropes.
Here’s an earlier post I made on the subject:
Personally, I like the idea that you’re free to define what shape of the arc you like, to fit your story ideas. Though I’m not sure you ever want it to be flat, except maybe for brief periods where the story is focusing on other things, or at the end if things have resolved. I believe the slope of the graph is a measure of the RS conflict, so flat means no conflict = boring. (Whereas a relationship suffering from stagnation, you would graph that as a downward slope.)