Will my Engaged Audience metric always be larger than my Active Audience metric?
Yes. Your engaged audience is a combination of your active audience and your prospects.
Active audience is defined as the number of audience members who commented, liked, discussed or shared at least one piece of content during the selected time period.
A prospect is someone who has left their email address via a profiling form/question (one type of content goal). As completing a content goal is one way for users to interact with your content, a single user performing this action is counted towards each of the two metrics.