Well, just because the sprinklers are capable of covering the zone with an inch of water doesn’t mean it is. If Rachio calculates the soil is 70% hydrated, it may choose not to water or to water only a little. If the reality was that it was only 20% hydrated, then it would have made the wrong choice. That’s the simplest explanation.
Likewise, if Rachio thinks that by watering for four 15-minute periods, it will go from 40% hydrated to 60% hydrated, but the reality is that it goes only to 45% hydrated, then again, it made the wrong choice. That’s also a somewhat simple explanation.
There’s also the possibility that there is simply some sort of disease in that area: cinch bugs, Brown patch, etc, that is killing the grass and giving the illusion of dehydrated soil.
So it comes back to:
1) how do I measure the hydration of the soil to verify Rachio’s calculation of “before” moisture.
2) how do I measure the hydration of the soil to verify Rachio’s calculates “after” moisture.
Assuming one or (more likely) both of the above is incorrect, then how do I feed the info back in to / correct Rachio appropriately?