***Rant Alert***
The first thing you need to understand is that FPI and S&P+ along with many other statistical models don't necessarily take account of what actually happened. They take data inputs than simulate what the model says SHOULD have happened. IOW, they value simulation over reality.
How else can one explain the utter stupidity of their rankings at the end of the 2018 season, after all the results were in? At that point, S&P+ ranked Texas as the #35 team in the country, 21 spots behind Washington with the same record and a weaker SOS, 20 spots behind 9-4 Pedo State and 15 spots behind 7-6 S Carolina. It's a model so grotesque that it ranked 5-7 Ole Miss one spot below 10-4 Texas. To top it off, the same "model" rated 2017 Texas higher than 2018 Texas. Those fools need to pull their heads out of their spreadsheets and look around at reality.
FPI, while still moronic looks like Deep Blue compared to the dumpster fire of S&P+. They ranked Texas as the #19 team at the end of the 2018 season. How on earth they think the #19 team could split with their #5 team and utterly dominate their #3 team is a mystery but whatever. One thing that computers can't do is recognize that the Texas team that destroyed Georgia in the Sugar Bowl was not at all the same team that lost to Maryland to open the season. Humans can see that, which is why the coaches and sports writers both had Texas at #9.