I worked as a landscaper and landscape supervisor in Tucson, AZ for twelve years, installing several dozen miles of drip irrigation supplying several thousand plants. I also spent two years at the University of Arizona Agricultural Extension in Marana studying irrigation and horticulture.
A typical dripper applies water onto a single plant ar a rate of .5 to 2 gallons per hour. After the irrigation cycle is complete you have a patch of moist soil about 10" in diameter and about 18" deep for the small dripper, larger for the higher rate drippers. The boundary between moist soil and dry soil is quite sharp and well defined, and beyond that boundary the soil is bone dry. I doubt you will find a climate more arid and hot than the Southern Arizona desert, so I'm not prepared to accept your theory that water moves away from the plant because the climate is arid and hot and the surrounding soil is dry. That is simply not consistent either with my education, nor with my twelve years of experience.
One of the problems we encountered was layers of compacted sandstone called "caliche," which is impervious to water. When we hit such a layer we had to either punch through it for drainage or lay a drainage line to drain the plant hole, otherwise the plant would die because water would stay in the hole and drown the plant. To test the drainage we would fill the plant hole with water and leave it overnight, and when we found it still full of water the next day the soil surrounding the hole would still be bone dry. The water would not have penetrated the surrounding soil more than an inch or so, even after standing in the hole for eight to ten hours.
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