[Theme: Sensible WP] Problem with post header!

I have a problem with the featured header image of a post, I get this: https://modernthemes.net/wordpress-demo/sensible/2014/12/03/how-to-join-a-guild/ as it should be. I want a custom image, and not the same as the featured image I selected. So, can I change the code?

This is the code right now:

get_header(); ?>

	<?php if (has_post_thumbnail( $post->ID ) ): ?>
		<?php $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'single-post-thumbnail' ); $image = $image[0]; ?>

    	<header class="featured-img-header" data-speed="8" data-type="background" style="background: url('<?php echo $image; ?>') 50% 0 no-repeat fixed;">
    		<div class="grid grid-pad">
        		<div class="col-1-1">
					<?php the_title( '<h1 class="entry-title">', '</h1>' ); ?>
        		</div><!-- .col-1-1 -->
        	</div><!-- .grid -->
		</header><!-- .entry-header --> 

		<?php else : ?>

        <header class="entry-header">
    		<div class="grid grid-pad">
        		<div class="col-1-1">
					<?php the_title( '<h1 class="entry-title">', '</h1>' ); ?>
        		</div><!-- .col-1-1 -->
        	</div><!-- .grid -->
		</header><!-- .entry-header -->

	<?php endif; ?>

Thanks!