| The way I look at mobs vs AoE spells is that you are cramming 48 lets say commoners into a 20'x20' square.
technically a fireball covers that are completely if positioned somewhere within the mob, however it is somewhat tricky to actually pull that off in practice (due to mass of bodies etc) and so it is more likely that the fireball will detonate in the first rank or two of the mob. while this will deal a lot of damge to the nearby mooks, at least some of the commoners will be protected somewhat by the mass of bodies between them and the fireball. | 
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