background pic

hm – maybe a little jQuery could help.
We had to set the min-height of the wrap_all container to the header hight.

Can you try this in child-theme functions.php :

function set_wrap_all_height(){
?>
<script type="text/javascript">
(function($) {
        $(window).load(function() {
            var headerH = $('#header').outerHeight();
              $('#wrap_all').css({
			    "min-height": headerH, 
			  });
        });     
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'set_wrap_all_height');

but there is a little time-shift till it works – so maybe a DOM Method will be more effective.