I don't know why people still argue about this, just build a 15k/10k arena, set prices according to the league.
In top league you set prices 20 for bleachers. Then set prices for lower tiers accordingly. What I mean is, if you're selling 13k bleachers you set your LT prices so you sell about 7k. If you're selling 11k bleachers, you set LT prices to sell about 9k. If you're selling 17k bleachers, you set prices to sell 3k lower tiers.