wpkg --instdir ...
The --instdir option let you enter the path to the installation directory. Note that the first time this path needs to be initialized with the --create-admindir command.
Note that when you use this option, it needs to be exactly the same each time you do an installation to the same target. It is advised that you use the --root option instead if possible.
The installation directory is where the files in the data.tar.gz tarball get extracted. By default it is the empty string which means the root path is used as is and the installation directory ends up being your system root ("/") directory.
IMPORTANT DETAIL
In case of a MS-Windows environment, the drive is not specified by default, therefore the current drive is used.
If you specify the installation directory with the --instdir option, you may also want to make use of the --admindir option to ensure that the correct packager database is used when working on that target.
Note that multiple targets may use the same --instdir option, but not the same --admindir option.