The <small> tags are inserted when the table is built in the /includes/classes/order.php file. Be careful altering that script.
It might be wiser to simply redefine the <small> formatting in your email template's stylesheet instead. Since that template is self-standing, altering the styling there won't affect other places on your site or other emails anyway.

ie:
Code:
SMALL {font-size: 12px;}