I've made a 21x 21 Iron farm, via Avomancer's design on YouTube, with only a slight alteration to the 5x5 farm area in the middle. Got my villagers inside okay, but they are not panicking from the Zombie sitting in the back. I assume it's a line of sight issue, I just need help with this. Just registered on the Forums recently, so I don't know how to link pictures.
Even with only a single tier (4 pods), the output is insane. The thing about is zombie is bouncing up and down in a bubble column, so line of sight is constantly broken and re-established. The other designs I tried with zombie mostly stationary did not work nearly as well.
With out pictures its hard to tell. I've done a version of this farm a long time ago, but have moved on to smaller quicker farms (that are virtually just as effective) Wattles has a really small compact iron farm I recommend. When I ran into a similar issue it was with the spacing above their head. I had put a slab above them but they didnt have enough space to stand on their beds, so raising the 'ceiling' up another half block did the trick.