Thanks for the information about the ATL international arrival area. I came through ATL today; plane landed at gate in E concourse, and as noted above, connecting passengers were sent to E for immigration/customs, and non-connecting passengers were sent to F.
To my surprise, there now is a PreCheck lane in the E international TSA checkpoint. My last trip through here was in April, and there was no such lane then. So it appears that ATL has been "improved" for the international TSA checkpoint.