On reassembly, I could engage either one of the two ears, but not both at the same time. _Lifting_ the antenna plate slightly with a paperclip bent into an “L” and inserted through one of the holes close the the center of the curved edge did the trick for me.
On my late 2012 Mac mini, I could not slide out the lower drive without removing the logic board; the memory cards were in the way. Radioman’s suggestion may work for some disks, but not for mine.
On my Late 2012 mini, the antenna plate connector is covered by part of the case. But, as FinnCrisp888 said, there is actually no need to remove the antenna plate at all; just carefully fold it back to expose the bottom drive.