What BritMum said, but you'll find that you will want to bulk out your meals with superfree anyway.
For example:
If you have spaghetti bolognaise, you only get 86g extra lean beef mince for a HEb. This isn't much, so you'll want to fill it out with superfree.
If you were on EE, there is nothing really stopping you from having 200g extra lean beef mince, and so the 1/3 superfree rule is imposed to try and stop you doing that.