Concave is for absorbing, convex is for repelling. Basically, you have been using an absorbing mirror in a dangerous direction for you and absorbing that qi.
As for the pa kua, it has specific applications and there is an early and later heaven version which all have different applications. Using them without knowing about that can have negative effects as well.
Another point - no one really recommends using a pa kua for repelling negative directions. They still contain vital energy in the overall setup. But if you want to neutralise killing energy from the east, then it becomes applicable. These days Feng Shui practitioners have reverted to five element theory again because it allows them to promote more elaborate cures. For example, if you want to neutralise a killing from the east, use light (fire) because the incoming energy is wood.
Last edited by KWLee; 10/22/11 05:13 PM.