It is preferable not to position the mirrors on the South west walls. Positioning of mirrors in this direction bring unrest in the marital relationships. Problems like over expectations from the partner, wastage and losses happen. Some times it also brings fertility problems in the couple. Problems pertaining to beauty will also arise if the mirror and table are placed in that direction. It is said to be caused due to the extension effect of the mirror.
Instead you can place it in the north eastern wall to bring in positive energy and lot of good health.