I am so glad to see people asking questions about HR training as I am also new to this. I have read several articles online, and like them and coach AJ mentioned, it takes time to get it right. I have also talked to other triathlete friends who are more experience in this subject and they also said the same, it takes time.
This is the perfect time of your training to test these thresholds so that eventually you can find the correct one for you. Remember, they are going to be different for everyone. My plan is to take 2 HR test this week to see how my numbers vary.
Also, I just read the article coach AJ shared on how to calculate your HR zones in Training Peaks and it was super useful. I hadn’t set it up myself and every time I finished a workout using my Garmin, it automatically uploaded it to Training Peaks and it kept changing my HR threshold.