I just installed an NH-L12. Is it supposed to sit tight on the CPU when the screws are all the way down, or is it ok to be able to rotate the heatsink a few mm above the CPU? The later is what happens with my PC.
More often with some specific TIMs (such as the AS 5), and particularly when there's a tad of it in excess, you can *vey slightly* (1-2mm) rotate the heatsink base over the CPU heatspreader, either on the left or on the right (I mean, when the cooler screws are all the way down).
Anyway, you may easily double check your build by heating the CPU (Prime95 small FFT or IBT would work well, in case).