Most probably because of the use of rep dedup. However I don't recommend to use any of the predefined freearc templates except for fa-store and fa-min inside of diskspangui because settings will not be the same as if you use them by freearc directly.
Example
Both archives were made with freearc ultra template (left: freearc, right: diskspangui)
Freearc templates inside diskspangui will not be using predefined arc.ini settings from freearc installation folder and will not apply on different file types, hence the ratio difference.