Armor class doesn't really get explained properly. Are you using mage armor on your Wizard? I had to tell my friend to use it because he just didnt know. He was having the same problem and it got better when he started using it. Not just because he had more AC, but because they seemed way less horny for him. I guess because he was harder to hit.
Your AC is generally 12 without it, 15 with. Its a lot of difference.
