Dueling D6's: Combat Odds for 6-sided dice

I've been working on a design recently in which I am thinking of using a pretty standard style of dice-based combat resolution. I first saw it in the game Mystic Wood, then in Talisman, and in a similar pirate-themed game called Sword and Skull.  Each player rolls a die and adds a bonus to it; high roll wins.  I did the math (not hard math) to figure out what a 1-point or 2-point advantage is worth in this scenario. I knew it wouldn't be linear, but I was curious how it looked.  The zone for ties gets smaller as your advantage increases, and a +4 isn't too different from a +5 in terms of results except that you can actually lose a +4 battle a fraction of the time. Anyway, here are the results.