We'll start off discussing this issue with the Dr. Occult story, "Vampire Venom". Occult is the first man in comic books to deal with vampires (and this is his second outing against them!), so this strip should be seen as authoritative on the subject. We see that vampires can appear from out of nowhere (probably had been in gaseous form), and that they can have bat wings even when in human form. It turned within sight of their graves, they flee back to their graves rather than fleeing further.
This page of Johnnie Law supports an idea I've been having for an optional rule, where a head blow would have a chance of temporarily knocking out someone, This would have to be entirely different from the hit point mechanic, where being reduced to zero hp means a long recovery. Perhaps the attack roll would have to score 5 or more better than needed to hit, with the stated indication of going for a head blow, and the target would have to fail a save vs. science or be rendered unconscious for only 1-20 minutes?
This panel with "constant firing" is making me think of an optional rule for suppressive, or covering, fire. It would keep combatants from being able to move through an area, while not directly targeting any particular combatant.
(Scans courtesy of Comic Book Plus)