How to add data to event template using filter?

I’m trying to use ‘eventorganiser_posterboard_item’ filter to add / change thumbnail size and maybe some metadata my code looks like:

/**
 * Add variables to event organizer posterboard templating 
 */

function kc_add_posterboard_vars($event) {
	$event['event_thumbnail_medium'] = get_the_post_thumbnail( get_the_ID(), 'post-thumbnail', true );
	return $event;
}
add_filter( 'eventorganiser_posterboard_item', 'kc_add_posterboard_vars' );

Thanks, fantastic plugin!