There really are no values to adjust. Gasoline has a fixed value as far as how much energy is available in a gallon, and a kilowatt is a fixed value for electricity. Unless you have some sort of special ability to increase the energy stored in a gallon of gasoline the answer is no. The Volt is just giving you information based on how efficient you are driving on electricity, and should gasoline be equally efficient (currently about 30% efficient), that would be your MPGe or equivalent. If you're looking to increase or decrease your MPGe reading, adjust driving more efficiently, or less efficiently.
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