FWIW, I couldn't quite make sense of the questions in here, but you can pretty much disregard temperature drop across the radiator. At least in water cooling, the flow rate is high enough that the drop across most radiators is only fractions of a degree.
Really doesn't matter which fan is more powerful on top or bottom, but there is a difference in distance from the radiator.
Besides air flow and volume, there is also an air turbulence effect that makes extreme shroud depth worse than placing the fan closer to the fins. About 30mm is about ideal, more depth than that and you'll loose efficiency.
I don't think there has been much testing of this sort of parallel fan setup, but it would be a similar pressure drop vs PQ of the fans. If the radiator is restrictive, you would likely net more flow from push pull which is essentially series vs shrouded parallel system.
That parallel system and overly deep shroud would also loose that proximity turbulence gain.