T4 does have its own CBP area. I went through it late last year, coming home from London.

Here is what I suggest: Get the AA app, available free from the usual app stores. The app has a function where you can check flight status. Check the flight on the day of travel, and it will tell you which terminal to expect the flight on that day. It will also tell you if the flight is on time, early or delayed so you can plan accordingly.

You can get the same flight status info from the aa.com website.