Ok I found it,
it is in the product handler. So for the default product type it is in
/admin/product.php
line 249
PHP Code:
$contents[] = array('text' => '<br />' . TEXT_HOW_TO_COPY . '<br />' . zen_draw_radio_field('copy_as', 'link') . ' ' . TEXT_COPY_AS_LINK . '<br />' . zen_draw_radio_field('copy_as', 'duplicate',true) . ' ' . TEXT_COPY_AS_DUPLICATE);
Add the third boolean argument of true to the radio button you want to be selected by default. (and just pass two params to the one you don't want to be selected)