The reason why the Coyote brush has such large root system is the dry climate in the chaparral. By having large root system the plant is able to get moisture from places that are further away from the plant itself.
If the Coyote brush finds itself in an area where the climate is much wetter, with higher levels of moisture, than it will certainly undergo so changes to adapt to the environment. The biggest probability is that the plant will have smaller root system, but be able to grow more. The reason for that will be that the higher amounts of moisture will enable the plant to get enough water without any problem, so a very large root system will not be needed. Also, because of the higher amounts of moisture the plant will be able to grow bigger as it will not have to restrict itself because of lack of water and nutrients.