For example, sitting on Feng Shui, Geng Xiang and You Mao, and Geng Xiang on the compass should correspond to A, why Geng Xiang and You Mao?

You say that only if it is wrong. Geng corresponds to A. Yes, the sitting direction of the house, such as sitting in A to Geng, can also be said to be Jiashan Geng.

And "concurrency" refers to the situation where two people are sitting in the wrong direction. If Jiashan is 80 degrees, it is close, while "concurrently" is miscellaneous and impure. In the Kong Xuan school, building a house is considered unfavorable, and at the same time, it is necessary to replace the stars with something, which is relatively troublesome.

There are too many other related things, so I won't explain them one by one.