I could not find in joint editor anything responsible for this strange behaviour. Anyway If you scale all fingers and thumb, hand looks ok. Only problems are small bulges on index and pinky - see pic (scale 90)

You can do one more trick. Load Koshini.obj, with 2 magnets make hands smaller, save obj as a KoshiniX.obj and hack cr2 file changing obj name. It is best solution, but I hate fix joints in all fingers what is necessery after such operation. It is quite easy but I'm too impatient. Fortunately you must fix joints in 1 hand only and after use symetry "do you want to copy joint zone's setup also?" - "YES" :)