I think PieFed can currently only handle a very specific chunk of Mastodon toots which somehow fit into our concept of communities. It can't attach toots anywhere if there isn't some group connection. To my knowledge neither do we do user following in a way it'd show up in your subscription feed. You can however go to a user's profile page and click the bell icon and you'll get notifications for their posts. That's probably not going to help here, since your posts aren't there in the first place.

I'd be nice, though to fully support Mastodon. And the developers are aware of that.