In the same folder as preferences.txt you may or may not have a file named formatter.conf. It is this file that controls the actions of Auto Format
Here is mine
# This configuration file contains a selection of the available options provided by the formatting tool "Artistic Style"
# http://astyle.sourceforge.net/astyle.html
#
# If you wish to change them, don't edit this file.
# Instead, copy it in the same folder of file "preferences.txt" and modify the copy. This way, you won't lose your custom formatter settings when upgrading the IDE
# If you don't know where file preferences.txt is stored, open the IDE, File -> Preferences and you'll find a link
# 2 spaces indentation
indent=spaces=2
# also indent macros
indent-preprocessor
# indent classes, switches (and cases), comments starting at column 1
indent-classes
indent-switches
indent-cases
indent-col1-comments
# put a space after if/for/while
pad-header
# Move opening brackets onto new line
--style=allman --style=bsd --style=break -A1
# delete empty lines in functions
--delete-empty-lines
# Insert space padding around operators.
--pad-oper