I’m trying out those settings you suggested and it does seem like it would mostly solve the issue for me, but you can see from the volume of comments that I am not alone in being unaware of the magic combination of settings that would make the default behavior of the app less frustrating.
I think it’s still a good idea to either prevent the back button from taking the user from their Posts page to the Communities page, or to include a method of returning to the last spot in the Posts page.
Also, I just want to add that this is an incredible app and I really appreciate all of the work you put into this!