How do I know if my main character is... "main" enough?

I’m writing a story, narrated by a protagonist who lives with the action heroine of the story.
Imagine if Short-round narrated the story of Indiana Jones and the Temple of Doom. If I show lots of Dr. Jones and maybe only spend half of the book on narrator-short-round-protagonist, is that bad?
What if my main character isn’t the driving force in the novel, and simply exists in a world where driving forces work around her, and she ultimately takes part in the climax, is that fine, or awkward?