I have just created some puzzles, under the Your Puzzles tab, with the above description - where x is a number from 1 to 9. If you click the Open... button, you will probably see one of these: the one for your score level.
This uses the option to play a puzzle against only those players whose scoring history is similar to your own. This feature has not been used very much since it became available. I don't know if that's because people aren't interested in playing in such a group, or whether people are just not familiar with it. I've started up these nine puzzles to give the scheme a bit of a kick start.
If you try it out and like it, you don't have to wait for me to set up such a puzzle - you can do it yourself when you publish a puzzle.