The larger the allocation size, the fewer the files that can be stored in that partition.
Take a gander at your Video folder, set the view to details, then click the column heading SIZE twice - - that will cause a sort descending of the folder content.
An ideal size would be the AVERAGE SIZE(all the files therein) - - but there's not tool to find that number :sigh:
I would choose a number that best fits the most dominant size shown,