@HorsemenPod here’s my solution. 3 tiers and then the top 10 FCS schools go into tier 3. Ranking is from the SP+
Tier 1
Tier 1
If you are the bottom 5 of Tier 1 you get relegated to Tier 2. Bottom 5 of Tier 2 to Tier 3. Top 5 move up.
FCS stay in tier 3 unless they win the tier 3 championship.
FCS stay in tier 3 unless they win the tier 3 championship.