How to change the number of Administration Views results in the Drupal back end?
To my knowledge, there is no such thing as a "global setting" within Drupal administration (what you call "back end") to set such "how many results".

The only way to do so (assuming you use Drupal 7), is to perform these steps for each of the individual views where you want to set "how many results" you want:


Use the Views UI to edit the view.
In the 2nd column, within Pager:


Use pager:  use the options "Display a specified number of items".
Pager options: set the "Items per page" to "how many results" you want.