They are designed for that orientation. The fans on the outside of GPUs blow down towards the board, not up towards the adjacent cards.
My setup has only about 1.25 to 1.5 inches between cards and I have no heat issues whatsoever.
The exhaust comes out the sides of the assembly, like this:
That was an informative image, thanks.
So how come when you put your hand close to the fan you can feel the hot air blowing out of it, adjacent to the cards rather than from it's sides?
Generally, only old cards are designed that way. It's not in common practice anymore, AFAIK. Blowing hot air out the sides of the card seems kind of dumb, too, but maybe I'm just missing something. You want the hottest air out of the case ASAP, not blowing around inside the case, so most card manufacturers have the fans exhausting out the PCI slot. By having the fans "reversed," you get the added benefit of pulling hot air off the rear side of the card below it, quickly expelling it out of the case and possibly cooling its VRM a little extra bit.
ETA: there's probably a way to reverse which way your fan's spinning.... you could probably just reverse the wiring on the fan's power cable, assuming it plugs into a socket on the graphics card. Maybe dangerous.
