Pagination always only showing two pages?

I’ve created a paginated list of terms for a custom taxonomy, but the output for the page navigation buttons is not showing correctly. No matter how many posts per page I set, it always outputs two pages.

So with 6 posts and set to 6 per page, I see two pages, the second one blank. With 6 posts and 2 per page I see two pages, and there is no third page.

Can anyone see why this might be?

$posts_per_page = 6;

$page = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;
$offset = ( $page - 1 );

$categories = get_terms('prints_cat');

for( $i = $offset * $posts_per_page; $i < ( $offset + 1 ) * $posts_per_page; $i++ ) {
	$category = $categories[$i];
	echo '<div class="cat-preview"><a href="';
	echo get_term_link($category->slug, 'prints_cat');
	echo '"><h2>';
	echo $category->name;
	echo '</h2></a></div>';
}
unset( $category );

custom_page_navi();

And the code for my custom_page_navi() function:

function custom_page_navi() {
	global $wp_query;
	$bignum = 999999999;
	if ( $wp_query->max_num_pages <= 1 )
	return;

	echo '<nav class="pagination">';

		echo paginate_links( array(
			'base' 			=> str_replace( $bignum, '%#%', esc_url( get_pagenum_link($bignum) ) ),
			'format' 		=> '',
			'current' 		=> max( 1, get_query_var('paged') ),
			'total' 		=> $wp_query->max_num_pages,
			'prev_text' 	=> 'Prev',
			'next_text' 	=> 'Next',
			'type'			=> 'list',
			'show_all'		=> false,
			'end_size'		=> 2,
			'mid_size'		=> 0
		) );

	echo '</nav>';
}