If I am following this right, the tax calculation for the commodity value is being based off the region’s highest seller value, which seems to be a NPC outlier at around 1000% higher than the highest buyer price in the entire cluster.
POCO tax is a percentage of the games moving average value for the commodity. I don’t know that CCP has published the formula but it appears to be a fairly conventional 30 day moving average with a 3 sigma limit - outliers beyond 3 standard deviations discarded. If your regional price differs substantially from the New Eden average, the estimate will not reflect that,
POCO Tax is set by the owning corporation, and if it’s located in highsec also by concord, and can be set between 0% upto 100% (in highsec: 5% upto 100%, although the common tax is around 10-15%).