13th, that was the way I had been interpreting it as well.
Essentially, you specify an endpoint outside of 3" from the ashigaru and then the target model moves the shortest distance possible to that route. Add to the fact that "directly" has it's own entry under the push section, and it seems that this would be true.
However, I have a whole 3 games worth of experience under my belt, so I want to make sure I am interpreting things correctly.
I have been playing it the way Csonti suggested, because I wasn't sure. So, I think I may have been cheating myself a bit.