When attack is unblocked it becomes damage. In your example the four attack becomes four damage, which you reduce to two then apply to your armour. So you take one Wound.Notice the difference between reducing damage points and reducing attacks (Dodge and Weave).
If the enemy is brutal, 4 attack points become 8 points of damage, that then are reduced to 6. Which is not the same as reducing the attack by 2. In that case, you would have to assign (4-2)*2 = 4 damage points.