well i was now matched first against stef and then against a guy with lvl <10, so i'm pretty sure it doesn't work
Okay, thanks. I can see those games in the server log and there are at least two things going wrong. Some good matches are being prevented and some bad matches are being allowed.
The bad matches bug was a one-line fix for the server, so that's deployed now and you shouldn't have that problem again. The good matches bug is more mysterious and I'll need to gather some more information before I can track it down.
Until then, be aware that automatch with the Isotropish rating criterion will sometimes work incorrectly. That is, if you set L20+ or L20-30, automatch will sometimes screw up and refuse to match you with a L25 player who ought to be eligible for the match.
Edit: Found the problem. Only the beta version actually submits the user's Isotropish rating to automatch, so you can't automatch with official-version users when you're using isotropish criteria. The beta will go out in a couple days unless some giant new bug arises.