There is a good reason for that. Each device checks sensors in a certain order. Water sensors have the highest priority so they are checked first. In the case of the Dual Water sensor scenario, sensor number one is checked  first. If there is an alert to be sent by that water sensor, it gets sent. Then the throttling kicks in:  every device will send no more than one alert per minute to the cloud.  From there it will be sent on as SMS, email or pushbullet. So regardles of what the other sensors are showing, their alerts will be delayed for up to one minute - and then sent only if the first water sensor is dry.

So if your deployment scenario calls for two sensors of the Dual Water Alert to indicate critical water level notifications, it is recommended that Sensor Two is placed at a lower level than Sensor One.

When using Water and Temperature sensors, be aware that a wet water sensor will send an alert and may cause the temperature sensor alert to be delayed until the water sensor is dry.