functions.php

<?php

// Our large image size
add_image_size( 'be_large', 500, 500, true );

/**
 * Genesis Grid - Use different image on CPT archive
 *
 * @author Bill Erickson
 * @link http://wordpress.org/support/topic/filter-the-image-for-cpt-archive
 *
 * @param string $image_size
 * @return string
 */
function be_cpt_image_size( $image_size ) {
  
  // Only run on the 'image' post type archive
  if( !is_post_type_archive( 'image' ) )
    return $image_size;
  
  if( in_array( 'feature', get_post_class() ) )
    $image_size = 'be_large';
  
  return $image_size;
}
add_filter( 'genesis_pre_get_option_image_size', 'be_cpt_image_size', 20 );