I have turned Raincheck off because of the kind of “corrections” that it was doing. As far as I know, I don’t have the type of bird “rain” perching that you have experienced, so I haven’t noticed false rain on clear days.
Earlier this month, we had hard rains all day long, some of them quite localized. Sky reported about 1.5 inches. The official weather site for Boise is about 6 miles away and well into the desert. Officially, Boise had about 0.9" of rain for that day. Raincheck “corrected” my total to even less than the official.
Observationally, both my wife and I were sure that we had well over an inch of rain and perhaps even MORE than Sky had reported, not less.
So I just turned off Raincheck.
Like you I have no idea where Raincheck gets its data. Is it another PWS? Is it from the NWS official site? Is it from a site along a highway? It would be a MASSIVE help if we could drill down to see the source of the data that Raincheck uses for its adjustments (I cannot even call them corrections when they introduce errors instead of remove them).
Boise is right against the foothills of a mountain range. That means that there are several micro-climates. Precipitation often backs off of the foothills, meaning that the closer to the foothills the heavier the precipitation. (The NWS site is miles further away from the foothills than where I live.)
There are also areas where the winds are often higher than others because of how storms interact with the foothills.
One of the reasons I wanted a PWS was for the local (my house) weather, not a standardized set of data that might be from a different micro-climate a mile away.