Add archive settings default for a custom post type

sample.php

<?php
/**
* Add archive settings default for a custom post type
*/

add_filter( 'genesis_cpt_archive_settings_defaults', 'cpt_as_testimony_archive_settings_defaults', 10, 2 );
/**
 * Callback for Genesis 'genesis_cpt_archive_settings_defaults' filter.
 *
 * Add the custom settings default value for the post type 'testimony'.
 * 
 * @param  array  $settings  An array of settings.
 * @param  string $post_type The post type.
 * @return array             An array of settings.
 */
function cpt_as_testimony_archive_settings_defaults( $settings, $post_type ) {

    //* if the post type is 'testimony', add custom default settings
    if ( 'testimony' === $post_type ) {
        $settings['posts_per_page'] = '';
    }

    return $settings;

}