Dont really know why it is so small, but this is the relationship between first half points and point differential and W/L/T
I found the data game by game, this seems better as averages can mask an anomaly (e.g. NE going up by 35 in 1st half can skew there overall results)
You can see in upper left that scoring <=10pts in a half has a 34% winning. Go over 10 (usually starting at 13+) and that % jumps doubles to 69%
The total points while important ís still seemingly notstrong as margin. Go up by more than 1Td and teams have won 88% of those games
When trailing at halftime(Margin<0) there is only a 25% chance of winning. Tied is 50/50 (13/13). Only 40 games have been come from behind at halftime. That is surprising, but human nature will remember those games since they are likley more exciting.
Final chart to the right shows all team and the point differential in all of the wins. Only 4 teams have - point differntials (Jax, Dal, KC, Cle).