I don't know the answer to this exactly. You also have to take into account that monsters have block/evade. I'm not sure how that plays in. For example, guided arrow can hit a single monster either 6 or 8 times if I recall correctly. Bone spirit is similar. If an arrow is blocked or evaded on the first hit, will it have a chance to hit again or is the missile cancelled? I haven't done enough testing with guided arrow or bone spirit to know for certain.