FFT filter settings

It's not trivial at all - but to understand what's going on, you need to learn a lot about how digital filtering works, and things like window functioning. The bottom line is that all of the filters in Audition (and they don't all work the same way, or have the same fundamental characteristics) are already maximised as far as they will go - and that's absolutely down to the fundamental characteristics of digital filtering. To get anywhere with this requires a fundamental appreciation of the difference between recursive and non-recursive impulse filters (Audition uses both) and there's a lot of math involved.

A couple of resources: pdf about windows functioning and for general stuff, the wiki page about digital filtering here. 

I'm afraid that it's going to have to stop being a big deal for you, because there's absolutely nothing that you or anybody else can do about it. Incidentally the window size you'd need to get filtering down to 1Hz to work would require a significant degree of calculation on an extended slow-moving signal, and you'd need an IIR filter to do it, which would mean using the Scientific Filter in Audition. And you'd be into all sorts of other difficulties with it at that point, involving passband ripple, phase response, etc. There's quite a lot more explanation about all of this here in the online help.