Post Indexer - I need to index Post Meta for custom fields on a multisite installation

I am using Post Indexer to enable me to pull Testimonials from one main site and display a random selection of them on all of my network sites. However, the data for the testimonials is stored in custom fields attached to all of my posts, and when I query the indexed posts, network_get_post_custom returns an empty array, with no meta data. Am I using the wrong function to retrieve the meta? Or is it simply not indexed? If it's not indexed, can anyone advise me as to how to extend the indexing to include that data?

I also tried indexing a Custom Post Type (created using Pods) but Post Indexer wouldn't index it, and kept unchecking that box.

Any help would be great, thanks!