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Don't mean to burst your bubble, and I don't mean any harshness, but "heat rises" is not true when fans are added to the equation. The laws of thermodynamics are one thing. Forced airflow is another.
But the top fan may cause turbulence and restrict the intake to cooler fan. That is if cooler intake fan cannot suck the downward airflow in as easily... This can and does happen, but not saying it is happening in this case.
Again, I mean no disrespect.
Now, now, trolling via repetition?
Fans or no fans, hot air or liquid, has the natural propensity to rise.
It's called convection. If you introduce a fan into matters, you only create turbulence which gets recycled through your case and passed thru the heatsinks.
The coolest air by a narrow margin is at the bottom of the case, so take advantage of it and make this point your intake.
The single most efficient use of cooling fans is to exhaust at the top once the cooler fins have made use of the cool air from intake.
Fighting against warm air rising is possible, but why fight it when it can actually assist your case's cooling capabilities?