Cummins 8.3 litre emission control vs. oil consumption?

We are currently noticing an increase in oil consumption from these engines because of emission controls, although not outside the limitations still more than the pre-em. engines.
I am aware of retarded fuel timing which causes increased combustion temperatures also carbon being held in the oil nd causing it to break down.
However does anyone know of more scientific reasons for increased oil consumption? (the customer wants a more exact answer than the points above.

Thanks