The checkboxes for post types (at the top of the settings screen) just determine if the map editor appears in those post types, it doesn’t have anything to do with the custom field dropdowns.
One thing that sometimes prevents custom fields from appearing is that WP doesn’t consider the field to ‘exist’ unless at least one post has been created with that field. Do you have at least one post that actually contains the fields you’re trying to select? If not, you could create a dummy post with them to see if this is the problem.
Also, only standard WP custom fields are listed. Are you using a forms plugin or similar to create them, or are they standard custom fields?