Realistically even N/S effects the second processor that is further back. It gets first dips at the fresh air and shoots it towards the top basically making a wall of air. A photo of the motherboard in the case would likely go a long ways but it you truly want to optimize the airflow than typically ducting is necessary for the 2 of them to not interfere with each other regardless of orientation.
But this kind of thing is why rack mount servers often align the sockets parallel to the intake just to avoid all of this.
Actually, as I mentioned for one of the S->N case options, I'd run the rear 120/140 as an intake. That would point cool air directly at the "back" cpu cooler. E->W is the one that really causes problems for the back heatsink eating the hot air coming off the front one. But it's still the winning voted option for now.
I first read two sockets which to me is 2 cpu but I wasnt sure if it is then depending on the alignment of the cpus Iprobably would be doing the botoom to top or I guess you're calling it south to north
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