It uses file sizes which all fit into the SLC configured cache. In the case of your 512GB drive, that cache ranges from 76-6GB depending on how much of the drive is used. Remember, I own this drive, the 2TB version, and I know exactly how slow the drive gets after the SLC cache is filled after the initial loading of over 700GB of files, 100MB/s or less, and it's why Intel redesigned the drive so it does not slowdown until after 50%.
Intel 660p:
Intel 665p