I've always been baffled at how the sim handles relief pitchers in the playoffs. Just had a playoff situation where my closer didn't pitch in the first 2 games, then pitched 1 inning and 10 pitches (!) in game #3, and his stamina immediately dropped from 100% to 93%. Now theoretically, in real baseball, he would have had a couple of days off after the regular season ended, followed by 2 days (games 1 & 2) where he didn't pitch, followed by a travel day off. And of course, in real baseball closers often even pitch longer than one inning in the playoffs and come back the next day! What the **** is the WIS "logic" on what they do in this situation? Anyone?

All pitcher fatigue is based on a seasonal allotment of Total Pitches, calculated using their real-life IP and BB/K rates. When a team enters the playoffs, pitchers receive an extra bank of pitches. Playoff fatigue is calculated based on the new playoff amount combined with any remaining pitches left over from the regular season, if any.

But that still doesn't explain how a relief pitcher with about 4 days rest gets wiped out on 10 pitches. What happened to the "extra bank of pitches" and the regular season leftovers (not sure how many, but he pitched 5 innings less than in real life).

SIM innings don't matter. What matters is how many pitches he threw in the SIM season compared to his seasonal allocation. He can throw 5 fewer SIM IP than RL IP and still exceed his seasonal pitch allocation. You're also counting days of "rest" that don't exist in the SIM. The schedule for real baseball means nothing here. This isn't real baseball. You should be able to find the information you need here:
https://www.whatifsports.com/forums/Posts.aspx?TopicID=434633