This is a subject that has been around for a very long time. As has been posted in this thread, it is a complete waste of one's time and energy to attempt to rationalize the reason for the CWOP barometer readings to be so spikey and simply inaccurate. I have spent countless hours myself trying to set my VP2 barometer to a value that would fall within the CWOP Analysis ranges. It became an impossible task. I've found that when I set it close to a nearby airport setting and compare those two on a regular basis that my VP2 stays in sync with it but the CWOP Analysis readings are all over the place.
Some years back, the source of the "secret" analysis readings were changed to include many data sources that to me appear to be very unstable and of poor quality. Complaints to CWOP folks always comes back with an answer that says they have no control over those sources. Just looking at the analysis graphs clearly shows that spikey nature of the data. Normal barometer readings do not and cannot change with such rapidity except during major storms. So, find a nearby airport or source of quality barometer readings and calibrate your local barometer to be close to those and you should be fine. I do a check every week or so to make sure I'm not drifting. Occasionally, I get a surprise and see my CWOP quality has a green check-mark but not very often.