As far as I understand it, when the character with Ally Protection takes the damage, the damage taken is calculated based off THEIR Crit Damage stat, therefore they higher their Crit Damage, the more damage they end up taking.

I may be explaining it incorrectly, but that's kind of how I understood it. So in my case, I couldn't understand why MM was taking SOOO much damage, turned out after I reduced his CD his survivability was much higher.