An email response to the review from Jakob of Noctua, which I think he won't mind sharing with SPCR readers:
Thanks a lot for your nice review on the NH-U14S! We have linked it on our website right away as usual and I'm glad to see that the cooler has got your recommendation again.
I was a bit surprised to see that you seem to prefer the NF-P14 over the NF-A15 - if I'm not mistaken, pretty much all reviewers so far agreed that the A15 provides an improvement over the P14. Since you have the same concerns with different samples, I think we can rule out the possibility that you've got a bad unit, yet the temperature results you show actually seem to indicate that you got at least as good results with the A15 (and even better at 18/19dB). But I guess you just don't like its sound characteristics?
Also, one note on why we went for the slim design rather than for an asymmetrical one: We see the U14S as an ideal choice for LGA2011 which has RAM on both sides of the socket, so an asymmetrical design doesn't really help.