Higher membership levels can’t see content they should have access to

I’ve set up four membership levels. Level 1 has been assigned to a number of pages using the Content Permissions meta box on each page. In Members, Levels 2, 3 and 4 have all been granted access to Level 1 content (but not ticked in Content Permissions). Levels 2, 3 and 4 can’t access any Level 1 content, even though granted access in Edit Capabilities: Custom, unless I also tick the checkbox for those levels in Content Permissions. Do we also have to tick all the checkboxes for Levels 2, 3 and 4 on all those pages even with access granted already to Level 1? What are we missing here?