When I played ball, they only took the top four teams in the region. We finished sixth my junior year and the season after I graduated, they switched to eight teams per region.
Our school had never been to the playoffs before but then went about eight straight seasons.
Some of the funny things I've seen regarding teams making the playoffs:
Our league had a couple teams right on the DI/DII border as far as enrollment goes and another team that was DIV. One of the teams was barely DI, just by a couple students and they finished the season 9-1 and didn't make the playoffs. The DIV team that year went 4-6 and made the playoffs.
The first year my school made the playoffs, there was controversy over their opponent. The rankings came out and an opponent was named. The next day, it was determined that one school in the region had been using an ineligible player. Because those games had to be forfeited, a team that had only won two games, now won three games. The team that was in the #9 slot had beaten that team and they picked up enough computer points by this team now having three wins as opposed to two, that they were able to move up to #8. Definitely one of the wierdest things I'd ever seen or heard in regards to the Ohio playoffs.