Heh, well apparently I had an old version of nifskope, and I needed the latest to see what you guys are talking about.
But I still have no idea what the bounding box *should* look like. I'm not even sure I understand what I'm looking at in the animation window, and how the animation sequence distinguishes which part is the death part.
Ok, I've just taken a look and in the bounds->edit menu, set the z translation to 100, the radius x to 100, radius y to 90 and radius z to 100.
The area of the bounding box is the area which determines where you will hit the creature, not the actual mesh area. These setting should make the bat an easier target. Make a backup and try them out, you will see the difference when you enter these figures.