Alter The Related Portfolio Entry Thumbnail Size

// Alter the related portfolio thumbnail size
function my_portfolio_entry_thumbnail_args( $args ) {
	if ( is_singular() ) {
		$args['size'] = 'wpex_custom';
		$args['width'] = 50; // Enter the width you want
		$args['height'] = 100; // Enter the height you want
	}
	return $args;
}
add_filter( 'wpex_get_portfolio_entry_thumbnail_args', 'my_portfolio_entry_thumbnail_args' );