Enterpr1se on "[Plugin: Jetpack by WordPress.com] Tiled Galleries & Resize Image"

In the support document in Jetpack.com
http://jetpack.me/support/tiled-galleries/

It tell us we can add this to themes functions.php

if ( ! isset( $content_width ) )
    $content_width = 800;

In Media --> Image sizes
I had set the Large size image is 1024x1024
but the image will resize into 800 as the $content_width was 800, the setting in Image sizes will be ignored.

How to fix this problem?
Thanks

http://wordpress.org/extend/plugins/jetpack/