The way the original mod works is that it will calculate a random number between 0 and 100, and then compare that to the percent chance that an enemy will surrender based on their confidence. So if the random number is 11, and the enemy has a 10% chance of surrendering because they are foolhardy, they will not surrender, because the random number must be lower.
What I have done is modified the script in question so that when this random number is calculated, it has the difference between the player and the enemy's speech skill subtracted from it. So if in the example given above, if the player has a speech skill of 20, and the enemy has a speech skill of 15, that random number will now be 6, which means the enemy will submit.
I think this is a pretty balanced way of doing this. With the original mod's default values, foolhardy NPCs will still be difficult to make surrender unless you have a much higher speech skill than them. On the flip-side of this though, if a very cowardly NPC has a much higher speech skill than you, they might refuse to submit. I do find this a bit unrealistic, so there is some trade-off, but ultimately I prefer this because it makes it feels more RPG-like.
If the overwritten script is ever changed in the original mod, this will of course need to be updated, too.