5000 mile OCI, and even that is too long on an EB. I have a 2011 3.5EB F150 and I choose 5000 mile intervals. Experience shows that 4000 is about the real limit of the oil and fuel dilution.
I'd not stress too much on the oil choice and pay more attention to how long you use it. The 3.5 will last forever with good maintenance practices. However, many owners have timing chain problems before 100K if extended drain intervals are chosen.
Even so, I get the best results with M1, 10W-30 EP. Iron took a while to come down.
It's good to remember that fuel dilution is a moving target. As much of it can/will evaporate when the oil gets hot enough. Over time, what's left behind of the fuel is NOT OIL, but a sludge of evaporated fuel byproducts. Your dipstick may never read low, but the oil may be quite diluted with non oil components.
This leads to an oil that fails to meet test criteria, as you've noticed.
EDIT: Your engine is just fine.