I’ve been noticing that my ships will switch away from a heavily damaged target to a less damaged one when I have vulture set. I’d expect them to keep pounding the most damaged ship until it was destroyed before switching. And yes, all targets are in range. It’s annoying to have a fleet set to vulture not destroy a heavily damaged, retreating target in by switching to a healthy one before the job is done.
Using Cooperative in addition to Vulture doesn’t make a difference.