Not following your logic
64Kb - 50Kb = 14Kb wasted space
16Kb - 12Kb = 4Kb wasted space
rather than
(13 * 4Kb) - 50Kb = 2Kb wasted space
(3 * 4Kb) - 12Kb = 0Kb wasted space
I use large allocation units for volumes that handle large files, such as video. Though I have not studied NTFS, my assumption is that each allocation unit has a checksum and is part of a link list or file table to track the units that are occupied by a file. I conducted a couple tests with large files which bore out that a volume with larger allocation units was faster, both reading and writing.
If your storing on volumes as large as this article is talking about, it may not really matter. The allocation unit is part of the equation of how large a volume can be, which is why the minimum size increases as the volume size passes the thresholds mentioned in the article.
