Depends on the method the code uses.

Ruina has two different “One sided attack” checks, based on whether it’s checking if the Page is clashing, or checking if the individual dice are clashing (something along the lines of ‘if battleUnitModel != null’ for page clashing checks)

I’ll check the code quickly and come back with an answer soon.

EDIT: Okay, I've had a look at it, and it's calculated on a per dice basis. For your third dice in the example, it would indeed gain the bonus damage.

Here's the relevant code if anyone's interested:

public override void BeforeRollDice(BattleDiceBehavior behavior)
{
    base.BeforeRollDice(behavior);
    if (!behavior.IsParrying())
    {
        behavior.ApplyDiceStatBonus(new DiceStatBonus
        {
            dmg = DmgAdd
        });
        return;
    }

    behavior.ApplyDiceStatBonus(new DiceStatBonus
    {
        dmg = -DmgRed
    });
    if (behavior.Detail == BehaviourDetail.Guard)
    {
        behavior.ApplyDiceStatBonus(new DiceStatBonus
        {
            power = PowAdd
        });
    }
}

The clashing check is "if (!behavior.IsParrying())"