Thank you all for your replies!
I decided to try the test again with a longer warmup and running on a flat track. My target HR was 110 and the duration was 60 minutes.
For the warmup, I jogged slowly for about 20 minutes shooting for a HR of 100 BPM. The warmup was on gently rolling terrain near the track. This felt very easy. (See first image)
For the test, I started at an 11:40 pace with my HR pretty consistent at 110. I was able to keep this pace for about 2 miles (22 minutes) before my pace began to slow in order to hold my HR at 110. My pace gently declined for the rest of the workout and my PA:HR for the test was 10%. This test certainly looks more like classic decoupling than my previous attempts. Given these cleaner looking results it seems my AeT is indeed somewhere below 110 and I’ll try the test a little slower in the near future.
One point of confusion:
Some of you had mentioned that the test could be performed between 40 and 60 minutes. If I had stopped the test at 40 minutes my PA:HR would have been more like 6%. I’m going off of the number for 60 minutes, but does the duration at which you cross the 5% threshold come into your analysis at all?