Hello Aaron,
I don't know why I forgot this, but the iOS podcast app uses the content:encoded before the iTunes:Summary. The content:encoded is your blog post content. They use this because the iOS app can display some (not much) HTML tags, such as the <p>, <ul> and <a> tags. I am looking for our page on the subject but I believe Mike Dell documented this last spring for folks who have been confused by it.
Show description in iTunes Desktop: <itunes:summary> used. If not present, the <description> is used.
Show description in iOS podcast app (before iOS 11 release in Fall of 2017): <content:encoded> is used. if not present, <itunes:summary> is used. If not present, the <description> is used.
Show description (shown below the fold when looking at the episode) in iOS podcast app iOS 11+ (to be released Fall, 2017): <content:encoded> is used. if not present, <itunes:summary> is used. If not present, the <description> is used.
Show summary (shown near the top, just below the episode title) in iOS podcast app iOS 11+ (to be released Fall, 2017): <itunes:summary> is used. If not present, the <description> is used.
Show summary and description relationship in iOS podcast app iOS 11+: Text matching is used, if the first 20 words of the summary match the first 20 words of the full description, then when the user scrolls down the text will align with itself (hard to explain). If the text is slightly different, then the summary will be displayed separately. The summary is cut off if more than a few words, we do not yet know what is an optimal length at this time.
iOS11 information is subject to change as the current versions are "beta" and may be changed before released.
As far as other apps are concerned, we need the developers to respond how they handle the various RSS tags to be 100% certain.
Thanks,
Angelo