I think he meant putting a fan near the front of the case, blowing across the top (side without a fan) of the 290X. But in my tower case there just isn't room. I have an 80 mm fan arranged as you suggest, blowing across the short dimension of the cards onto the motherboard (the side case cover is off).
Exactly. The other configuration (parallel to the mainboard) has proven to be much less effective (at least in my case... And in my case he he ;-) )
I now have arranged a 12V 120 mm muffin fan, re-wired to use the 5V supply, to blow across the top of the 290X. This is in addition to the 80 mm fan which cools the 260X.
The 120 mm fan is not at the front of the case, rather sits on top of the card about 1 inch from the rear of the case. I can mine now at 540-590 MH/s without damaging my hearing (core=900 mem=750, case cover is off). Good Lord--you could heat a studio apartment with this thing.