Content-Encoding means page compression – gzip, deflate or none. More than half of all pages has this HTTP header included. It should move your position about 2 position up, when you have a lot of competitors. You must combine it with Vary: Accept-Encoding.
I wrote about this themes in .htaccess file and Browser cache.
Content-Encoding: gzip and positions on Google
No Content-Encoding HTTP header and positions