I need to have a different amount of posts per page on the first page that on the other pages.

For example, this is what I need

• Total posts: 6
• First page: showing 3 posts
• Following page: showing 2 posts per page

Here’s my code:

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;

$fp_limit = 3; // first page limit
$limit = 2; // following page limit
$offset = 0; // default offset

if( $paged == 1 ) {
    $limit = $fp_limit;
} else {
    $offset = $fp_limit + ( ($paged - 2) * $limit );
}

$args = array(
    'post_type' => 'my_post_type',
    'post_status' => 'publish',
    'offset' => $offset,
    'posts_per_page' => $limit,
    'caller_ get_ posts' => -1, // remove sticky post
    'paged' => $paged,
    'tax_query' => array(
        array(
            'taxonomy' => 'my_taxo',
            'field' => 'slug',
            'terms' => array('slug1', 'slug2', 'slug3')
        )
    )
);
$my_query = null;
$my_query = new WP_Query($args);

// basic loop
if( $my_query->have_posts() ) : 
while ($my_query->have_posts()) : $my_query->the_post();

...

endwhile; endif; // archive loop
if (function_exists('wp_pagenavi')){ wp_pagenavi( array( 'query' => $my_query ) ); }

wp_reset_query();

At first page in archive, this code assumes:

Well, 6 posts total and 3 posts per page. So I need 2 archive pages and the pagination I present to you is:

[1] [2]

However, any other page in archive the code assumes:

Well, 6 posts total and 2 posts per page. So I need 3 archive pages and the pagination I present to you is:

[1] [2] [3]

Need a little help to fix this.