Which way to mount the heat sink fan?

[Traxan]

I've been wondering if it's better to mount the fan so it blows heat away from the heat sink, or down onto the fins. I have the XP-90 with an 80mm fan. So, blow out or down?

 

[SketchMaster]

Take a look! it's in a book!

Now run befor the repost gang shows up!