Did Peter Jackson ever explain the Witch-King's flail?

Question

Thought about it while reading this question, specifically the quote in the answer:

He bent over her like a cloud, and his eyes glittered; he raised his mace to kill.

In the books, the Witch-King has a mace when he fights Éowyn. In the movies, he definitely has a flail and sword combo.

My initial thought was that Peter Jackson wanted to avoid too many similarities between Sauron in the intro to the first movie and the Witch-King in the third. Helmet aside, they'd look pretty similar if they had essentially the same weapon. But there are other characters with maces, too, notably Azog the Defiler, a character Peter Jackson himself invented, so clearly he doesn't seem to mind an enemy having a mace, unless they have a scary helmet, maybe?

Is there any official statement from Peter Jackson or another important LOTR figure explaining why the Witch-King had different weapons? Or is this just another of those "Hey, it's different from the books for no reason"?

Answer 1

As TGnat mentions in comments, there's a featurette on the Extended Edition DVD talking about the design of the Witch-king; the bit relevant to his weapon is on YouTube:

Although they don't answer this question directly, some of the images seen in the background indicate that they initially designed (and constructed) a more traditional mace, but the magic of design iteration transformed it into a flail (confusingly, everyone interviewed continues to refer to it as a mace, except for Lawrence Makoare at one point calling it a morningstar, which more accurately describes the initial design but it equally wrong for the finished product):

They mention that Peter Jackson repeatedly demanded the head be made larger, so my suspicion is that they transitioned to a flail partly because at a certain point the mace would have looked absurd, and partly because at a certain size it would have been impractical for Makoare to wield on-camera, something that he still ended up struggling with.

Jackson: In addition to the helmet, we also redesigned [the Witch-king's] mace. [...] And I looked at the first one that they built and I just said "it's okay but we need to make it bigger."

Daniel Falconer: Okay, so we made it bigger. And Pete came back and said "no, I need it bigger again", so we made it bigger. And everybody's going "oh my god, this is like, this thing's getting huge. It's totally impractical now." Well, it went from impractical to ridiculous

[...]

Lawrence Makoare: Some people call it a mace, some people call it a morningstar. Either way, I ended up calling it "damned heavy," 'cause it was damned heavy.

Jackson: It ended up being so large that you actually couldn't pick it up.

Answer 2

having some experience of thing I'm pretty sure that it was an aesthetic decision. Bearing in mind that John Howe, who is very knowledgeable about medieval arms and armour and a Tolkien expert was a senior concept designer on the film it is unlikely that it is just an oversight.

I imagine that the idea was to make the character of the Witch King more distinctive and give a strong visual indication of his power. In the extended DVD commentary they certainly acknowledge that it got ridiculously large but this is just one of those situations where the director has the final say on what works most effectively visually. It is certainly not the only example of style over logic type decisions.