The number of teams that make the playoffs is determined by your league. This can be modified anytime up until the playoffs begin.
Playoff seeding works differently for leagues with and without divisions.
Once a team is guaranteed a playoff spot in any league, they'll have an asterisk (*) next to their name in the league standings.
Leagues without divisions
In leagues without divisions, the top teams make the playoffs. To determine seeding, we look at the following in this order:
Higher Points Against
Overall Record takes precedence over points for (PF), which takes precedence over (PA). Tiebreakers beyond that is a coin toss or can be determined by another metric the commissioner sees fit via custom seeding.
So if you want head-to-head to be the tiebreaker, you can still manually put that team in the playoffs.
Leagues with divisions
In leagues with divisions, the winners of each division automatically make the playoffs.
In 6-team playoff leagues, the bye week goes to the 2 division winners with the best record, based on Overall Record > Points For > Points Against.
Any remaining playoff slots are filled by teams that did not win the division, and seeding is sorted by Overall Record > Points For > Points Against.
In a 4 division league, the top 4 seeds will always be given to division winners, while the remaining bottom seeds will be filled with non-division winners.
This can be customized by modifying the standings manually via custom seeding the week leading up the playoffs if you play by different rules.