For most people with ADS, it is common to jog-walk on their aerobic workouts even on flat terrain. Since your goal is to fix ADS, I would recommend staying below AeT. An occasional spike in HR above AeT won’t hurt but based on what you said if you do 10 steps walk/run then it is likely you will spend a lot more time in Z3.
Here are some resources for further reading –
Forum Discussion – ADS Slow Walking
UA Article – Slow Best for Fitness