The X ring is a solid metal ring that is (I believe) 1mm wider as to cut off all the airflow from the cap of the X. It's in case you have an atty that gets its own airflow. It cuts off the gap the stick ring will give you. I got one and it works like a dream. So your KFL will sit perfect on top with 0 gap.
You know, strangely I prefer that 'gap'. It matches the one at the bottom... and offers a more uniformed look. But yes, that's me; and it's purely a personal preference/taste.