Please don't create add-on.xml files by yourself, which is not required, since our installer will create the proper files automatically, and we might have updates that might fail because they assume the add-on.xml file is the correct one created by our installer in their normal position and with the default configuration.
I'm not saying there will *surely* be problems *now* ( maybe not for sceneries, but for GSX I know there ARE problems if the add-on.xml is edited ), but there might be in the future so, save yourself some possible troubles, and don't touch any of the files made by the installer.
The FSDT P3D4 installers are the most compliant out there, and are the most flexible ones, since they still allow you to install the sceneries everywhere ( as long all FSDT products are under the same root, everything is allowed ), so you don't really have any reasons to edit them.