gotcha, did you just get those graphics from google?
Ya I just google image searched a few pictures, just to illustrate. I find it's easier to help comprehend where your hot air is going.
I used to have two cards in one standard pc enclosure but it was impossible to cool, no matter what I do, one of the cards go above 75 degrees C (with 70% speed fan), so I have to shut it down.
I even tried installing 5 fast coolers (4000 RPM) 1 front, 2 at side over the cards, and 2 back taking the hot air out, but no go, the less worst solution was leave the case open, but still one of the cards remain at 68 degrees C or so.
68-75C is actually acceptable for a GPU, but you might try upping the GPU fan itself. Try increasing it from 70% to 90% and see what you get for temps.
In an open frame, try and work with natural convection currents you'll be creating in the room. That is, the hot up draft you are creating.
If you can get a fan below parallel with the motherboard, that will really help carry the hot air away from the cards and reduce air pressure surrounding them [simplified]. = easier for the card to exhaust more air.
The best example I've seen of that was Catfish, and his vertically mounted GPUs, seen
HERE. Imagine of those were stock blower GPUs, blowing the hot air up and away from everything. You would never worry about hot air circulation ever again!