Hint #1: The four long entries are not part of the meta. Focus on the title instead: what is 20% expressed as a fraction?
Hint #2: 20% = 1/5... concentrate on the five-letter words... say them out loud... do any of them jump out to you?
Hint #3: The hint at 64-Down is twofold, "gimme five" means you need five words total... and "up top" means you need to take the top letter from these five words (20% off the top)
Hint #4: The five 5-letter words are symmetrically placed... starting with 1-Down