Have a look online. If it was just the poster you replied to, your dismissive reply would have some weight, but it's them and hundreds of others. It is a known problem. Not universal by any means, but it seems far more common than with other heatsinks. Although that may be because people who pay for the best heatsink are more likely to notice such things. The concavity isn't visually obvious, but can be seen by the uneven dispersal of TIM if the heatsink is later removed or by resting a rigid straight edge on the bottom of the heatsink.
It's debateable whether it makes any difference to performance, though.
It's debateable whether it makes any difference to performance, though.
