Get a conditional to change image on header.

Hi, I’m trying to get a conditional to change the header image, I’m using Yoko Template and I’m not an expert on PHP, here’s what I’ve got so far.

if ( is_singular () &&
				current_theme_supports( 'post-thumbnails' ) &&
				has_post_thumbnail( $post->ID ) &&
				( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'post-thumbnail' ) ) &&
				$image[1] >= HEADER_IMAGE_WIDTH ) :
				// Houston, we have a new header image!
						echo get_the_post_thumbnail( $post->ID , array(1102,350), array('class' => 'headerimage'));
						elseif ( (get_post_image) ) : ?>
						<img src="<?php header_image(); ?>" class="headerimage" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" /><!-- end headerimage -->
					<?php endif; ?>

in the line
elseif ( (get_post_image) ) : ?>

I substituted get post image for “null” and I got the template to just show me the header image on the home page, what I want now is to get the conditional to show me another image for the rest of the posts, with reduced height to make it navigation-wise friendlier.

Thanks in Advance.