up against the larger one that is attached to the wall. it has been up for over a year and i haven’t had any problems. if you are worried about it slipping or sliding forward, you can place the mirror where you want and make a “stop” for it. you can do this with two tiny nails – nailed into the mantel top. let the nails stick up a bit and they will stop the mirror from sliding. you can also use double stick foam tape. cut a piece and tack it down right under the front edge of the mirror. the foam texture and stickiness will help it from 