Focus miss chance
I made 116965 attacks focusing the neck while using the focus special ability and missed 3989 attacks due to focus. This means that unless other factors are at play, focus neck imposes a miss chance of 3.41%.
I also get ~3% when focussing neck and so does my friend when they're on offensive tactics (I was on neutral).
The more interesting thing might be that I get roughly the same for focussing head. Head should be easier to hit, so if it gets the same ~3% then ~3% might be the lower limit of focus miss chance.