/**
 * Re-position featured image metabox from sidebar to central content area
 */
function change_meta_box_position() {

  remove_meta_box( 'postimagediv', 'post_type_here', 'side' );
  add_meta_box( 'postimagediv', __('Featured Image'), 'post_thumbnail_meta_box', 'post_type_here', 'normal', 'high' );

}

add_action( 'do_meta_boxes', 'change_meta_box_position' );