Use this code example to add custom data to the Statistics section in the monthly email.

add_filter('frm_summary_email_content_args', 'summary_email_content_add_custom', 10, 2);
function summary_email_content_add_custom( $content_args, $filter_args ) {
	$content_args['stats']['custom_block'] = array(
		'label'   => 'Custom data',
		'count'   => 10,
		'compare' => $filter_args['email_obj']->get_compare_diff( 10, 9 ), // 9 is the previous value to compare. Set 'compare' to 0 to disable comparison.
		'display' => '$10',
	);
	return $content_args;
}