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 probably should have mentioned that along with the fan blowing on the top of the cards, I have a 120mm high pressure fan blowing air out of the front of the case. I believe that makes the difference. Tons of heat comes off the rear of the cards and it gets pulled out by that other fan.
It probably doesn't help me that the fan in my spanking-new Corsair RM850 power supply died about 70 hours into the MAX-mining. So it is not pulling air out of the case. That's the main reason why I have the case cover off. And an 80 mm muffin fan blowing on the RM850. It's a very efficient PSU, the 80 mm fan blowing on its side is adequate to cool it even when the 290X is going full blast. This weekend I'll have to take it back to Fry's for an exchange.