One: because there is water in the kitchen and balcony, if it is not lowered, it will flow to the living room, and there is no sewer in the living room!
Two: it has nothing to do with the feng shui angle!
Three: when installing the door, there is a "water stop"
Why is it five centimeters? Suppose you forget to turn off the tap and the water flows to the kitchen floor. At this time, if it is not lower, the water will flow to the living room. But if it is only a few centimeters, the sewer pipe in the kitchen will be too late to run, and the water will flow to the living room. So 2CM is the most suitable!