Hi Anna,
Welcome. I'm glad you are finding my book useful!
Regarding your question about short distance shooting, the Korean bows can be used quite effectively with either a long or short draw--whatever someone feels comfortable with. First, though, there is no longer short distance shooting in truly traditional archery in Korea; however, some people/clubs sometimes set up short distance for special occasions and such.
Having shot both long and short distances with Korean bows, I can speak a little bit about what I found works for me. I think the biggest obstacle will have to do with archer's paradox (or deflection, depending upon the spine of the arrow), due to the short distance. For that reason, it is important that the arrow clear the bow directly upon release; in that way, the paradox (or deflection) will not be as exaggerated as it is when the arrow tries to bend around the bow. So, be sure to grip the bow correctly (diagonally across the palm, as in the book), give power to the lower part of the handle (pushing slightly upward) and, when you release, let the bow pivot in your hand slightly, with the string rotating away from your bow arm.
See how that works for you and please let us know.
Thomas