Maxxforce Engines and Fuel Dilution?

Have been collecting, reviewing oil sample data from a group of buses with the Maxxforce International engine, 2009 buses. Fuel dilution in every bus is 6% or greater with services being done at 1/2 the expected cycle. To keep the fuel dilution below 4% this customer would have to service their engine every 3 to 4,000 miles. Anyone else seeing these kinds of results? What about your other engines?