Thaumcraft Flux from a crucible

So I am building a tower on our server and one of the request that have been made of me was to keep the roof open above the crucible to disperse the flux. My question is this. Do I need to keep the entire roof open, or do I need to just have a single open block above the crucible, or can I just put a roof on my tower above the thaumcraft and have the walls surrounding the room have open windows, IE, a open areas with nothing blocking them.

Thanks for any help you can give

Nash