I was installing an SSD in my mini and when I got to this step, an issue came up. The two 6.6mm screws on the antenna plate screw into one side of, and secure, the hard drive. The problem was the SSD was thinner than the original hard drive, so when I tried to reassemble, the hard drive sat too low for the screws to reach it.
Here's how I got around the problem. I loosely attached the antenna plate to the hard drive, leaving plenty of wiggle room between the plate and the drive. I also left the two stand off screws on the logic board off to give me more wiggle room there.
With the SSD attached to the antenna plate, I carefully connected and stowed the Bluetooth cable. Using the antenna plate as a handle, I was able to guide the SSD into the hard drive mount. Once in place, I tightened the 6.6mm screws more, which raised the SSD to the proper level.
After insuring that the screws all lined up, I installed and tightened the logic board, then the other antenna plate screws.