The reason it is not recommended to have a mirror facing the main door is because the mirror pushes away all the good feng shui energy that is about to enter the house.
In feng shui it is considered that the house absorbs energy (Chi) through the main door, similar to a human face absorbing nutrition through the mouth. This is why the main door is often called the mouth of a house in feng shui.
Distance will only slightly change the effect of the mirror facing the main door, so if you have a mirror directly facing the main door, best feng shui advice is to remove it.
If you cannot remove the mirror, for example if the mirror is built-in and you are renting the place, or if you have mirrored closet doors facing the main door, then you have to look for creative solutions.
Feng shui always works best when it is applied in a creative and subtle way. So, cover the mirror with some creative applique, for example, or paint over it with a washable paint in a great color.
Other suitable feng shui solutions:
- Have a lush, big plant in front of the mirror.
- Tastefully hang a suitable size piece of art over the mirror, be absolutely sure it looks good.
- Have a tall enough piece of furniture centered on the mirrored wall. Again, you have to be sure it looks good.
- Have applique, or decorative stickers on the mirror (Ikea has some great wall or mirror stickers.)