In our Wi-Fi version of the 10.5" Pro, Apple left some mysterious plastic blocks where the LTE antennas might be found.

To add to the mystery, these weren't present in the Wi-Fi 12.9" iPad Pro...

We are speculating that it adds support to the display assembly, as opposed to being empty space as seen in earlier iPads.

Nothing much to see until we remove the large shield covering the logic board. Time to unzip it and see what we find.