Hits, 5% is exactly what JSB specs are, if you find a better way of doing it, go ahead and start a new business.
what you see is a Gaussian distribution, seen everywhere in the nature.
in a working airgun, when everything works even 5% weight wont make 5% POI change, for reasons unknown. but for sure it is not only the hammer and regulator balance.
regarding Weighing Pellets, usually people resort to do this because they have a poorly performing PCP. Barrel or mechanical issues.