Hi Learner,
I agreed with you that is not very clear.
Based on SAP note 727719 you need to have an active variant defined. So, even if you have external capacity option in APO if you have an active variant the heuristic will take in consideration the capacity variant defined in APO.
From 727719:
"One of the capacity variants of a resource can be defined as anactive variant and then it shows the available capacity of the resource which is relevant for planning. If no active variant is defined, the standard capacity or external capacity of the resource is used."
Thanks,
Regards, Marius