Sorry it’s been a while since I got back to you on this.
landing-pages is a post type and each landing page is a post in the post type. Basically all you need to do is copy the rules used by ACF for either a specific post or a specific page and alter them so that they are looking at the post type used by the other plugin.
If you look in the ACF4 code in the file /core/location.php you’ll find all of the standard location rules and you can copy the ones you need and make the needed adjustments. Actually, you can use the same rule match function used for matching a post, you just need to add the other filters for adding the choices.
Hope that helps. Hope this helps.
