This article should answer your questions –

Heart Rate Drift: A Functional Measure of Aerobic Fitness

Once you have done the test, if your heart rate drift is less than 5%, then the initial heart rate (at the end of warmup and beginning of your test) is your AeT. When I did my test, I had no idea of my AeT. I used the MAF formula (180-Age) to get a rough estimate and then repeated the tests till I got a heart rate drift of <5%.

Training Peaks will not calculate your AeT.

If your initial heart rate for the test is far below AeT, I think your heart rate drift will be much lower.

I hope this helps. Good luck with your test.

Say I am going at snails pace and am certainly within aerobic intensity, would that not produce a different heart rate than a pace that is at the very top of my aerobic threshold?

I believe so.

My fear is that if I’m not running right below my AeT (which I dont know yet) then I wont get an accurate result of this test. Am I completely misunderstanding how this works?

Determining AeT is a trial and error process, so it’s okay if you don’t get an accurate result in your first test. After a couple of tries, you should have a good estimate of your AeT and then you can structure your training accordingly.