Losing the metal clips that you're talking of (marked in green on the bottom photos) is the top reason for abnormal Wi-Fi operation after reassembly.
Here are two images, which I shot, that better depict the cause of the issue. Once you lose that piece, you have no option but to order a replacement cover.
[image|119844|size=thumbnail]
[image|119843|size=thumbnail]
In case the images don't work here, here's an external [http://imgur.com/a/ytep8|link].