use coorindate break surface to control the height of the surface. The tool Tilt/Decenter element can assist to do so fairly easily, once you set the decenter x/y as variables you could make them changed during optimization.
Hi Gracewu, see the picture below to show the principle of it. '=$`NG8l n8Qv8 Set cooridnate break surface to surround the mirror and then make decenter X and Y variable. >G|RVB