You need enough PEI stories to cover the major dimensions without forcing one story into every question.

Quality and flexibility matter more than building a huge library. A small set of strong stories can often be adapted to different prompts if the underlying example genuinely fits.

For a PhD, useful stories can come from research setbacks, influence without authority, conflict, leadership, collaboration or difficult decisions.

Prepare the facts deeply enough that follow-up questions do not expose gaps in the story.

For what it's worth, My first answers were way too long because I kept explaining the research context. Might vary by office though.

imo My first answers were way too long because I kept explaining the research context. That was my experience.