How to Specify the Order of Custom Column and Existing Column

Can you please take a look at this code and let me know how I can change the order of added custom coulmn. As you can see I am adding 3 columns DifficultyLevel, ShortTitle, ShortText but these are all adding to the end of column

Name | Date | Project | Level | Stage | Phase

but what I want is display them in this order

Level | Phase | Project | Name | Stage | Date

add_filter('manage_posts_columns', 't4a_remove_unwanted_columns');
add_filter('manage_posts_columns', 't4a_add_post_columns', 5);
add_action('manage_posts_custom_column', 't4a_get_post_column_values', 5, 2);

// Remove unwanted columns
function t4a_remove_unwanted_columns($defaults){
    unset($defaults['title'],$defaults['date']);
    return $defaults;
}

// Add new columns
function t4a_add_post_columns($defaults){
    // field vs displayed title
    $defaults['DifficultyLevel'] = __('Level');
    $defaults['ShortTitle'] = __('Stage');
    $defaults['ShortText'] = __('Phase');
    return $defaults;
}

// Populate the new columns with values
function t4a_get_post_column_values($column_name, $postID){
    if($column_name === 'DifficultyLevel'){
        echo get_post_meta($postID,'DifficultyLevel',TRUE);
    }
    elseif($column_name === 'ShortTitle'){
        echo get_post_meta($postID,'ShortTitle',TRUE);
    }
    elseif($column_name === 'ShortText'){
        echo get_post_meta($postID,'ShortText',TRUE);
    }
}