I don't think it's fair that a mw arbalest can shoot through a mw heavy norman shield, plain and simple.
I think that crossbows of any sort shouldn't be able to penetrate through shields if :
a.) Opponents shield is heavier than 6-6.5 weight
b.) Opponents shield skill is 5 and higher
c.) a combination of both points above
Overall i like the idea of crossbows being able to shoot through shields, it adds variety and depth to the game more or less, but i think it should be seriously balanced. This tweak will also benefit the ballance of sword&board classes, because currently the majority of shielders prefer to use lighter shields (elite cavalry, knightly kite/heater shields). This change would make heavy shields a more viable option.
Your thoughts ?