shield acts as arrowmagnet

[Maroon]

The "arrow magnet" effect is not effected by the bow or the arrows you're using, but by the shieldskill of the bot you're shooting at. Aside from increasing the amount of damage his shield can have, someone's shieldskill also increases the coverage the shield gives you. This is probably meant to show the fact that people who are more skilled with a shield can throw their shields in the path of incoming arrows, but since an animation for that would be too much for Warband, they've stuck to making the shields magnets.
Most bots in NI do not have much shieldskill afaik, which is why you can still shoot over their shields. Some bots have more skill than others, though, and are therefore harder to shoot over the rim of their shields.