Well, there is something special when one can feed at exponential distances, by just knowing what a person looks like. Well, there just may be something about making a person gasp, losing their breath when a psi-vampire walks up to that person, without even intentionally trying to do anything. There is a difference between consciously feeding versus subconsciously feeding. Those psi-vampires, who don't know how to mechanically feed, feed by inducing some sort of stress upon others, and when these psi-vampires do feed they may not fully know what they doing, but their behavior may be out of touch. Then there are those who can and do consciously feed, either by inducing stress, simply being in the presence of another, or mechanically choosing to feed.
There is a reason why I like talking to Pisces people, because they are those special people who can sense things, on a level, so therefor they usually understand, when a psi-vampire shows them a thing or two. Then it's like the psi-vamp doesn't have to start all over and explain his or herself. The only thing that a psi has to say is that he or she is a leaking bucket, and that they can't help it sometimes that they feed the life force out of others. Then they might get into a conversation about thought forms.
Now, that I look back at one psi-vampire, this one guy wasn't stealthy nor tactical about how he was feeding. So this guy I am thinking about was probably the most obnoxious psi-vampire I've ever seen. To me that is kind of funny and it points out a few other concepts, in the way that this guy was. He was a psi-vampy, but he didn't really know how to feed in other ways, when he needed to feed, because he didn't exactly know himself.