How to get the meta title of a page configured as blog (loop)

I’m using a function to print the titles for every type of content. I also configured a new metabox in the posts and pages to enter the title tag.

This is part of the function to print the titles:

//...
elseif (is_page() || is_single()) { //Page and Post Title
    global $post;
    $metatitle = get_post_meta($post->ID, 'metatitle_value_key', true);
    if ($metatitle) {
        echo stripslashes($metatitle);
    } else {
        the_title();
    }
}
//...
else { wp_title(''); }

It works perfect for posts and pages, except when I select a static home page and the blog page (it’s a blank page created previously). Thanks to the last else it prints the normal title of the page ‘Blog’, but it doesn’t print the metabox with the metatitle ‘My metatitle box’.

I thought it was ’cause of the post ID, so I separeted is_page() and is_post() trying to get the page ID out of the loop, with this code $page_id = get_queried_object_id(); but this one didn’t work for me. The following code is what I have:

//...
elseif (is_page()) { //Page Title
    global $post;
    $page_id = get_queried_object_id();
    $metatitle = get_post_meta($page_id, 'metatitle_value_key', true);
    if ($metatitle) {
        echo stripslashes($metatitle);
    } else {
        the_title();
    }
} //...

What can I try to do that? Probably the problem is due to the way to insert the metabox, it uses $post_id every time. Anyway I’m not sure, ’cause it works for both: posts and pages.

//...
elseif (is_page() || is_single()) { //Page and Post Title
    global $post;
    $metatitle = get_post_meta($post->ID, 'metatitle_value_key', true);
    if ($metatitle) {
        echo stripslashes($metatitle);
    } else {
        the_title();
    }
}  elseif (is_home()) { //Using is_home for the blog page

    //And using get_queried_object        
    $page_object = get_queried_object();
    $metatitle = get_post_meta($page_object->ID, 'metatitle_value_key', true);
    if ($metatitle) {
        echo stripslashes($metatitle);
    } else {
        the_title();
    }
}
//...