The moisture sensor in the ground should be the definitive source right? Regardless of what other events happened (daily observed weather, irrigation events, and precipitation) if the sensor says the moisture is at 40% then that must be the case. Especially since weather stations are miles away - rain at the station may not mean rain at my house. I would say that all events should matter, but ultimately if the sensor says there is X amount of moisture then that should trump other events.
I do see depthOfWater - but I wonder how to calculate that based on the reading from the sensor.
BTW - I really appreciate your willingness to have this discussion!