What happens is fuel evaporation while sitting , fuel slosh and any slight backfire or spitting backwards when cranking sends fuel into the foam that is the filter media in those things. So you basically have a fuel soaked wet sponge sitting on top of your engine.
All we need is an ignition source and we have a spectacular underhood fire. But don't worry about it,,, it's not like anything underhood is hot or causes sparks or anything like that.. <grins>
Edelbrock did change the media in the ProFlo filter to dry out and not be quite the 'wet sponge' of the original media. But the fact still remains you only have around 35-40 square inches of filter media for ALL of the air to enter the engine. Compared to nearly 150 square inches of filter surface of even a short 3" x 14" diameter round filter.
Also putting the filter media so close to the top of the carb inlet creates UGLY turbulences of the air entering the venturi (does nasty things to the consistency of the a/f the carb delivers)