Broken up and scattered along the reef would make it easier to find, IMO. If there were a million pieces scattered about, chances are you would have found more than one. Every colonist would have had an Alcoa frying pan. However, the one piece you found looks like it was separated from the airplane intentionally.
Floated or flew* away and sank is the real needle in the haystack, and I think that is what Ballard is counting on. He's probably thinking it's either in a 40 square mile chunk of ocean West of Niku, or a slightly larger chunk of ocean East of Howland.
*Flew Away and Sank Theory = The 7 site has produced only items that would have been on Amelia Earhart's person or in a small cosmetic bag, including bits of the actual bag (zipper, bit of unidentified fabric, bead), and skeleton of one person, leading me to believe that they lost the Electra and its supplies rather suddenly. Maybe the Electra landed intact and with some fuel on the reef. With the airplane still flyable, they did not unload supplies. Fred, injured and delusional from heat, attempted to take off, lost his landing gear (Bevington Object) and wound up in the drink off the reef. 12 hours or so later, the Navy flew over and found nothing.
Floated away works the same way - Tide comes in after a few days on the reef and carries away the airplane and Fred, unexpectedly.