Transitions in story format

Over the years I’ve read many books that follow a certain formula. The book opens at the inciting incident and provide vague details about it. Then we go back in time and for about half of the book, we hear the story of how the protagonist got to that point. At about the 2/3’s mark, we reach the inciting incident and we get the rest of the story. It’s a formula that I’m sure someone who has degrees in creative writing knows the name of. Think every book about the Vampire Lestat and you’ll know what I mean.

I’m having trouble with the transition from the inciting incident to the beginning of the story. Does the inciting incident need to be a prologue, something many people argue as being “bad writing “. Is it enough to say “Three years prior…”? Any advice on how to make this transition?