Like I said, it's all about average PPO2. In a multilevel dive, If your OC backgas PPO2 averages out to around 1.3 for the bottom portion of the dive then we'll be about the same. However, if you're carrying gas that will give you 1.4 for a deep excursion but we spend the majority of the dive at a shallower depth you'll be running a less than optimal mix and your average PPO2 will be less than mine and my deco will be more efficient.
In practice, however, when I dive in mixed teams we typically have about the same deco schedule because they are carrying the most efficient bottom and deco gas (as a trade off their logistics is more complicated) and their turn pressure dictates the dive - even though I could spend hours longer in the water. Which is the real benefit of CCRs - BOTTOM TIME