In geomantic omen, water flows from both sides of the mountain and meets in Fang Kun. Why the pattern?

In geomantic omen, water flows from both sides of the mountain and meets in Fang Kun. Why is it a pattern-there is a pattern of double-washed plowshares. There is a pattern of water holding dragons. The pattern of double-washed plowshare is that the trend of the mountain is pointed at the intersection of the last two waters, and the water comes out from the most pointed position. The pattern of holding water dragon is that the direction of the mountain is obviously wider than the pulse width at the end, and the water flows out from the intersection of the two sides.