[Batfish]

As far as heat dissipation, I'm sure someone here could give you an entire technical lecture on it, but I'm better at the simple approach.
Your 9920 is a good example to use in an explanation since it has a heat sink on it already. The purpose of the heat sink is to draw/conduct heat away from the component(s) that is heating up. This is why, generally, heat sinks have many fins; these fins provide more surface for the heat to be released through the sink. Logically speaking, if you can keep the heat sink cooler it will be able to gather more heat from the component(s) and help the component(s) to stay cooler as well. This is why air flow is essential, and why the heat sink isn't inside of the shrink wrap. Forced air flow (fan) enhances the effect by moving more air past the heat sink allowing it to dissipate more heat.

One actual argument to back up the "masking" concept can be made by approaching it a different way. If your setup is wrong, a fan won't fix it. For instance, if you're geared wrong and pulling too many amps, a fan won't increase the amp rating of your controller, but it may let it run a couple minutes longer before it thermals/fries.

Almost all of the advice for cooling on this forum comes with the premise that the setup you're using is appropriate for the vehicle.