FacetWP – distance in DESCENDING order

<?php

add_filter( 'facetwp_filtered_post_ids', function( $post_ids, $class ) {
    $params = $class->ajax_params;
    $sort_key = empty( $params['extras']['sort'] ) ? 'default' : $params['extras']['sort'];

    if ( 'distance_desc' == $sort_key ) {
        // @TODO reverse $post_ids
    }
    return $post_ids;
}, 12, 2 );