I recently noticed that posts from my app were going to all-friends even when I requested they be public. Through the response to my bug report (https://developers.facebook.com/bugs/191063590970288) I learned about the "App activity privacy" setting buried in the user privacy settings but I don't see anything in the FB developer docs about this. Even if it's not something an app can request a default permission for, it would be nice if there was some mention of it on the privacy or post documentation pages.
Anyway, does anyone out there know of a way to request "public post" permissions?