I think Scott might have more insight than I do- but here’s my two cents. I’ve spent some time playing around with these concepts and training and noticed a few things- I was lucky enough to test myself on the same lab equipment that Real Rehab has a few times.
a.) This might vary from person to person, but I find that from measuring myself and from seeing a few other people’s results- my aerobic system takes a little longer than 10 minutes to fully “boot up” and I had the most accurate results after a good long 20-25 min warm up at really easy intensities. The fact that your fat burning goes up after a few minutes at the lower end of your HR range makes me wonder if your warmup was too short.
b.) I was able to push my fat burning ability all the way to max HR effort without getting a crossover point mostly due to playing with my diet (I did this out of curiosity). But I was pretty slow because my training volume was on the lower end at that point- so the lab results didn’t correlate well to what my treadmill testing results were (using a HR monitor and looking for the 5% HR drift w pace)- which did line up nicely with the nose breathing results.
c.) Unless the tech took into account your current training goals and training history, I wouldn’t pay too much attention to the suggestion to add 1 min intervals- that seems kind of random unless there’s a really good rationale.
d.) As for your body going into “starvation mode”, I’m not aware of anything that supports that training in a fasted mode will cause that. Maybe if you were living all the time in a fasted mode it would… but you are just fine going for a hour jog in the morning before breakfast. 🙂