With a difference like that, I would probably slow down in either case. If you’re trying to do an AC capacity type workout, crossing over AeT will start to limit the efficacy of the intended goal of the workout whereas slowing down below AeT would still get you the benefits you’re after for that workout.
For a workout like that (assuming AC Capacity) during Base building I think even a well-trained athlete would opt to slow down because runs of that type done during that time would need to be closer to zone 1 anyway to avoid going too fast and leaving them too depleted to get the most out of more intense workouts.