Bad “read more” behavior, trying to fix by inserting tag

Here is the solution I used to force the “continue reading” link to jump to the top of the text, just below the title

I first modified an existing “more” tag to a specified one –
in my style’s functions.php, at its end I added

// ALTER MORE TO JUMP TO SPECIFIED TAG (which is above post text in content-single.php)
function alter_more_jump_link($link) {
    $moreoffset = strpos($link, '#more-');
    if ($moreoffset) { 
      $link = preg_replace( "/#more-[0-9]+/", "#more-jump", $link );
    }
    return $link;
}
add_filter('the_content_more_link', 'alter_more_jump_link', 20,1);

To insert the specified “more” tag after the title,
in my style’s content-single.php, after line

</header><!-- .entry-header -->

I added

<span id="more-jump"></span>