OK, so as indicated in A Word or Two on Parrying, it becomes important to be able to read your opponent.
If they are attacking full out, do you want to parry? Or do you want to try to hit them before they hit you?
Fortunately, it isn't too difficult to anticipate the actions of monsters. They tend to attack full out, with little thought for self defense. But when dealing with human opponents or the like, it seems like the higher level character should have the advantage.
One way to handle this is to make the lower level character declare his actions before initiative is rolled. The higher level character can declare his action after initiative is rolled. It would be interesting to bring Charisma into the mix, allowing for more charismatic characters to more easily fool their opponents in battle. Maybe Wisdom helps you see through the charade.
Some things for me to chew on...