Please do your research better. A FAE bomb casing is discarded before the bomb explodes as by then it´s no longer relevant. The fuel in the casing is blasted into the air around it, that´s what makes the initial "cloud" part in the vid with the demolished house, the cloud is then ignited. There is nothing what so ever containing the fuel cloud, ergo it´s an open air explosion. If you tried igniting the fuel inside the casing, you simply cant make it explode because it lacks an oxidizer and has less than a billionth of the surface area needed to explode.
This is actually another bonus for FAE munitions, because the casing has no other strength requirements than being able to hold the fuel and other parts inside it until it´s expended.
And i might also add that the reason the fuel in FAE is such complex stuff is simply because the munition is very poor at causing optimal dispersion of the cloud, so fuel that is more lenient to poor dispersion is needed.
Magic has no such restrictions.
Yeah. Now, consider this, the vid above uses 3kg. I got almost the same explosion from using ~0.1kg at near optimal dispersion. I would guess 0.2kg should equal that explosion without problem. So at the very least they´re doing the boom at a 10-1 inefficiency because of the lousy dispersion.
Necessary to get full damage, or you end up with half or maybe just fire damage or something.
Ezz is talking several hundred kg of flour/dust so... Potentially, ridiculously much.
And this is where guidelines kinda break down and cry, because you only need to add a few Magnitudes for size to this to start looking at mushroom cloud level devastation. You actually start getting similar effects on a minor scale already with Ezz current spell. Fireball-shockwave-reverse shockwave... Everything but the radiation.
Anyway, for the sake of not blasting game balance into a complete wreck, starting out in the +30 damage area or thereabouts is probably a good idea. Or maybe +25 with a successful finesse roll and +10 without or something.