for the ringwraiths, Plan A every time they do anything is probably to try to panic their prey into making bad decisions.
Yes, I suppose you
could characterize "fall down on your face, curl up, and put your arms over your head" as a "bad decision" in a case like that. . .
Back in The Shire, they were looking for information, though. Is it because a hobbit that's gibbering in panic may not be able to provide any that they turn it all down a few notches there? Or are they actually not capable, in The Shire, of instilling such panic? The Gaffer gave 'em lip. So did Maggot. I've always had the impression that Fatty Bolger escaped panic by a hair's breadth only, or maybe it's fairer to say that he was able to channel his panic into a useful running-away: that's still a lesser level of panic than curling up on the floor. I subscribe to Corey's theory that the power of The Shire is damping them down.
In Bree, Harry was shaking with fear after talking to a Rider. But their relations with Ferny and the Southerner were a bit different: in The Shire, they offered gold, but nobody wanted it from them. I think Ferny had no such qualms!
Later, of course, they get upgrades and Monty Python jokes about their greatest weapons apply.
Ok, enough musing. Bottom line is I like this insight, too. The Ringwraiths aren't stupid, but they've gotten into the habit of intimidation, and optimal battle tactics aren't necessarily a priority to them.