Probably windage. The crank will create a mini-tornado in the crankcase which will pick up oil and fling it around the crankcase. Having a lower oil level should reduce that.
One of the benefits of a dry sumped car.
would all the extra oil cause a turbo overboost situation?
(asking for a friend)
It could, if the piston seals start to let a *lot* of oil mist through, cause the engine to start running all on it’s own. This was sort of a problem with early DPF equipped diesels cleaning the filter, they’d add extra fuel, which wouldn’t always burn off (especially with colder engines and lower loads) this would then run down the cylinder walls and dilute the oil, and eventually over fill the sump. Which would eventually cause the issue.
Or, you’d get so much diesel in the oil that it’d run past various seals if the fit wasn’t perfect. THEN you could get the turbo issue (overboost doesn’t really describe it well).
There were several recalls for this (change the oil, better software to determine when to inject extra fuel).
I’ve heard that the oil that came out of the sump was, in some cases, more than 50% diesel.