Change number of posts tax and terms of custom post type

I’m currently using this code to display a custom number of posts on archive pages and taxonomy pages of a custom post type. I really thought this was ok, but somehow it doesn’t work.

For instance this page: https://www.dierbaardier.nl/dier/

add_action( 'pre_get_posts',  'set_posts_per_page'  );
function set_posts_per_page( $query ) {

    if (is_tax(array('soort','ras','kruisingofbastaard')))
        $query->set( 'posts_per_page', 12 );
    return $query;
}