My take on the actual chances are 20% automatic and 5% missing the playoffs, which suggests 38.75% chance of promotion. This broadly aligns with the best odds you can get (5/2).
Before the weekend, I only had us with a 10% chance automatic and 3% chance of missing playoffs, suggesting a 31.75%...
Probability doesn't quite work like that.
Assume your probabilities are correct. Assume there are 100 possible outcomes. 25 are automatic promotion, then 75 are playoffs. We then have 1 in 4 of the playoff outcomes that get us promoted. So there are 25 + (75/4) = 43.75% chance of promotion...