Surface flatness of 6-inch diameter mirrors at the Navy Prototype Optical Interferometer is specified to be within 32 nanometers over a 5.4-inch diameter circle centered on the mirror. The current mounting technique is to use three spring plungers applied to the back surface of the mirror, near the perimeter edge, thereby pressing the front surface against three small diameter Teflon® pads directly opposite the plungers. The pads have the effect of dissipating the deformation effects within the 5.4-inch diameter region. This paper describes the effects of varying the size of the pads, from a 7/32 inch diameter pad to a point-type contact such as a ball bearing. Experimental results using a phase shifting interferometer are presented, as well as finite element analysis results.