The sensor can only measure the humidity of the place where it is inserted but not an large area. It cannot measure the soil moisture level within a few meters of the surrounding area. However, the general humidity of the soil where sensor is inserted does not have much difference. So when inserting it, we suggest find a place which represents the average condition for your zone, not place sensor in special places, such as edges, pits, blocked places, etc.
The distance between whisperer and Sprite does not matter. Please make sure you sensor is not too far away from the wifi router. You sensor and Sprite should work under the same wifi, so if you do a test and you phone is able to connect to your homewifi, your sensor should be OK.