My Filco wobbles on my desk but doesn't wobble on my g/f's desk, so I think my desk is probably slightly warped. BUT if you flip over your keyboard you'll notice two mini dome in the middle top and middle bottom. I suspect those dome touches the table to make it wobble. (there's more of those dome on the left and right corner too) So I'm guessing you can either:
1. Sand off those domes and let it purely sits on the rubber legs. (But if you plan to resell it then it might be a bad idea)


2. Fold a face towel in half and put it under the keyboard. I'm using this method now it also absorb "desk echo" and make your keyboard sound better when you type. Drawback is it look a bit ghetto depends on what colour towel you put down. But I highly recommend trying the towel method first it makes my keyboard sound so much better.

EDIT: Added Pictures. Also after some thoughts, probably don't sand off the domes at the bottom (Method #1). They're probably there for a reason so let's just leave it at that
