Yes, it is correct to put the DN partition in the device CSS. By default the CFA CSS does not get concatenated with the device CSS. However, there is a service parameter that will allow the CFA CSS to be the same as the line/device CSS. The service parameter is called "CFA CSS Activation Policy" and needs to be set to "With activating device/line CSS" to allow this behavior. See the link below.
One additional question, How would you configure CSS's in the case where you want to limit the CFwdAll to a "lesser" COS (Line can call LD, but only want to allow CFwdAll to Local or Internal numbers)?