He learns about his responsibility as heir to the throne.
In the sentence above, the 'as' prepositional phrase follows the noun 'responsibility'. Initially, I thought that it might complement said noun by describing it, and perhaps it is describing the nature of the responsibility. However, 'he' is clearly the heir to the throne in question, so I'm not sure. If it is describing 'he', shouldn't it be beside the noun?
As heir to the throne, he learns about his responsibility.
This is another example, which moves the prepositional phrase to the front. Correct me if I'm wrong, but I always had the impression that fronted prepositional phrases function adverbially. However, this seems to modify 'he' again, not 'learns'.
How should this be broken down?