I ran the model for 2008-2016, but only took the Brier score for 2016.
Code:
100% 0.203023179
90% 0.199892169
80% 0.197203494
70% 0.19494991
60% 0.193105915
50% 0.191632998
40% 0.190483555
30% 0.189609862
20% 0.189008209
10% 0.188894837
0% 0.190274481
Interestingly, these results imply that 10% mean reversion would have been ever so slightly better than 20% for the 2015-2016 offseason. I don't want to draw any larger conclusins though since 2015 was a weird year.