So, at one point I think there was an external antenna planned for the Tachyon, without it I am kind of scratching my head now on best placement of the device.
I was planning on connecting the Tachyon through the HAT to a daughter board which has a bunch of connectivity / ICs on it. It looks like the WiFi antenna is right next to the HAT connector. One side of my device is basically a display, which may block signals. The HAT would sandwich it between some copper.
Instead of a board sandwich through the HAT I could use a cable, and leave the board somewhat more open to the enclosure.
Below is my current thinking, which is to still mate the two devices with the HAT/Header. I could also flip the whole things the Tach is “facing the back of the screen and on the left” if that makes sense. My concern is I have found screens tend to just kill wifi signals being a sheet of metal on the back.
As much as I found the external antennas on the earlier devices annoying they made this problem a bit more straight forward 
Let’s call this the “fun one” as I was playing around keeps the wifi a bit more close to the edge of the enclosure. I should note I do need access to both of the MIPI ports.
Lastly, the board does not seem to get super warm, but I am now getting to the overall board layout stage and am curious about thermals, does the Tachyon normally need active cooling? a heat sync? or just ambient, if something more than ambient does one side get hotter than the other?