I'm not sure how much "bonus" I get, since I can prove that my gas engine burns significantly more fuel and costs more per mile as a result. The FSC, as I understand it, is per mile. If it were per gallon, then yes, I might get a bonus.
When I was a courier, running a route: 200 miles average per day. Cost of the Sprinter, fuel and 300 a month car payment combined, at 21 miles to the gallon, came to 100 dollars less a month than my old Ford, which got 14 miles to the gallon cost for gasoline alone. Right now, the price of diesel and gasoline are real close per gallon in my neighborhood, so the Sprinter would kick the ford's rear in cost. Now, tell me again about that "bonus".