Lots of useful information on rainfall here: Anybody Had any rain Since firmware update v94 (don’t let v94 in the title put you off)
Essentially, every SKY unit is still using the same calibration curve, despite the fact that the exact method used to mount the SKY has a large impact on its sensitivity. This is making some too sensitive, some under sensitive and some just right. This will be fixed when WF roll out the continuous learning scheme for rainfall, and the calibration becomes specific to each station.