This formula basically means that if you have less than half of your stat points into [[Dexterity]], you will have a lower block rating than your shield displays, but if more than half of your stat points are in Dex, then you will have a higher blocking %. Blocking is capped at 5% minimum and 75% maximum and displays if you hover on your Defense in the Character window. Sorcs and Necros who do not devote considerable resources to raising their dexterity will almost always be find their blocking at 5% past a very low level above Clvl 50, so should pick shields based on their magical bonuses, not for the blocking percent.