I don't know what the micron ratings are between the 2, but as said above, I'd expect the rear filter to be doing most of the work. If anything, I'd think the service intervals would be reversed.
That's how I treat my 07 with an aftermarket filter downstream of the OE filter. OE at 5-7micron absolute is catching all the "big" stuff AND some of the small stuff. 2nd filter is just sweeping the floor for the primary filter. I do primary every oil change, secondary every other. But my intervals are roughly half the miles. My filters are cheap. New truck owners are getting ripped off. Half dozen mfgs can make 2 micron filters good enough for semi trucks but the automakers design $100 filters???
Btw, to ftd, I was quoting about $100 online for BOTH filters. Dealer price is much more.
I learned a long time ago, squeezing all the life out of diesel fuel filters is not a good practice.
And remember, the DIC is calculating filter life based on gallons or fuel or engine hours, not based on how clean the fuel you put in the truck was.