They are set to 100 for two reasons,
1) This is the WINDOW in which a reversal (press Y) can occur for both user and cpu whereas the reversal rates are how often they reverse. I found the matches have been flow and back-and-forth sequences when set this way
2) I have reversal prompts turned OFF, so it gives me a little more leeway when it comes to reversing a move.
In the past, I set this at 100/100 mainly to multi-man matches. I'll experiment this year to see it it matters for 1-on-1 matches as well.