Hello,
There's no option to set reverse order with addChart. We have added a task to be added to the next release of phpdocx (there's no release date yet).
As your license has an active LUS, if you need this feature for your current work, if you open a support ticket (https://www.phpdocx.com/support) (although we have checked it may require about two days of coding and testing, a pack of three tickets would be enough as it will be added to the next stable release for general use), the dev team will do the needed changes to the chart classes and send it to your e-mail.
Regards.