I would like to propose a different tie breaker procedure for your consideration if you don't mind.
My proposal would base the tie breaker on the prowess of the individual posters who are in a winning position versus basing it on the cumulative points scored by the winning teams throughout the year (something that is totally outside of the poster's control)
I propose this:
Going into the final game of the season, have the posters who are tied for the lead, and those who are one game behind the lead, not only pick the winner of the game, but also the margin of victory. To avoid further ties, a condition would be that no poster could pick the same winner by the same margin of victory.
After the last game:
First consider the picks for each poster (without considering victory margin). If there is still an overall tie, then consider the winning pick and margin of victory for each of the tied posters. Whoever is closest to the actual margin of victory is the winner. Since each poster would have a different margin of victory, there could not be a further tie.
Say the last game is the Pioneer Bowl featuring
Team A vs. Team B
Going into this game, 2 posters are tied for the lead with a record of 56-10, and 3 posters are one game behind with records of 55-11.
All remaining posters would be out of contention for the championship.
The 5 posters would then pick the winner and the margin of victory as such:
Poster 1 (record 56-10): Team B by 5
Poster 2 (record 56-10): Team B by 3
Poster 3 (record 55-11): Team A by 14
Poster 4 (record 55-11): Team A by 7
Poster 5 (record 55-11): Team A by 17
The actual score of the Pioneer Bowl is:
Team A - 17
Team B - 10
First considering the winning picks the final records are:
Poster 1 (Picked team B to win) at 56-11
Poster 2 (Picked team B to win) at 56 -11
Poster 3 (Picked Team A to win) at 56 - 11
Poster 4 (Picked Team A to win) at 56 - 11
Poster 5 (Picked Team A to win) at 56 - 11
Now all 5 posters are tied!
Now consider the winning pick and margin of victory:
Posters 1 and 2 are eliminated because they picked Team B who lost!
Posters 3, 4, and 5 are in contention because they picked Team A who won!
Poster 3 Margin of victory: 14
Poster 4 Margin of victory: 7
Poster 5 Margin of victory: 17
The actual Margin of victory was 7 points
Poster 4 wins the championship because they are the closest to the Actual Margin of victory (0 points)
I hope that isn't too complicated. I just think that this tie-breaking procedure allows you to break the tie according to the ability of the posters to pick the games, instead of something the poster can't control (the total points the teams they picked scored throughout the season).