How rare is Indiana's poll ranking for a defending champ?

After achieving a perfect 16-0 record and securing the national championship last year, Indiana has entered the current season with a surprising ranking. The Associated Press Poll has placed the defending champions at No. 6, which puts them outside the top five positions. This situation raises questions regarding how frequent such a significant drop in poll ranking is for a team that previously won the national title and maintained an undefeated season during their championship run.