Apologies if I wasn't as clear as I could have been in my previous posts.
HIIT sessions burn a high volume of fat in proportion to longer, slower runs and they also bring about the 'afterburn effect' where a degree of fat continues to be burnt post-run.
So if you warm up and then spend, say, 20 minutes doing HIIT, you might burn in the region of 300 kcals - great! You've successfully burnt some fat. You're also knackered from the hard workout and it's not recommended to carry out an intense workout like this for another week or so. You might find that, the next day, you only run for half an hour because you need to recover, or you might even have the day off.
Alternatively, you go out for an easy-pace run for 45 minutes, burning (let's say) 400 kcals. You finish with some energy to spare then go out the next day and do the same session, burning another 400 kcals.
These numbers are, of course, general and just for illustration. The point is that a HIIT session is effective in terms of the time involved for that individual session but, across a week, it's the slower, aerobic zone sessions where the bulk of fat is burnt.
So if you run easy for a total of, let's say 3 hours, across a week, and you also have a HIIT session lasting 20 minutes, the HIIT session on its own might burn 300 kcals but the bulk of calories will be burnt with the slower runs which could total 1,500 - 2,000 kcals. It's simply because our bodies will allow us to do a lot more slow, aerobic running compared to HIIT workouts.