I experimented and think I figured it out…
If I use 'post_id' => 'options2' in acf_add_options_sub_page per your suggestion, then where corresponding options2 needs to appear on display is…
$featured_posts = get_field('featured_posts', 'options2');
This suggests I can use…
$featured_posts = get_field('featured_posts', 'article');
$featured_posts = get_field('featured_posts', 'report');
To display through my singular template fragment, showcase.php, I’m going to need to write a little piece to determine whether to call “article” or “report”.
You’re right, this is not at all clear from docs. You should write ACF: The Missing Manual.
BTW, I get a weird white screen when I save these options for the first time.
