Interval Training/HIIT Vs Steady: the maths doesn't square

seasoul

Hi,
people who support HIIT/IT vs steady peace usually refer to examples like the following:

Steady pace
- 30 minutes, 300 calories --> 50% fat --> 150 calories fat burnt

High intensity exercise
- 30 minutes, 450 calories --> 40 % fat --> 180 calories fat burnt

The big issue that I have is in the % used to support the examples (40%,50%..): who says that in HIIT you burn 40% of fat?
If HIIT is very intense you are likely to burn much less fat: if you burnt 10% fat --> the fat used would be 45 calories and in that case HIIT would prove to be the wrong choice if the goal is loosing fat.

Am I missing something here?
Cheers