The new definition of K used on Frau Putzer's 2018 X3 makes more sense: Lower the K to lower the displayed MPG, increase the K to increase the displayed MPG.
But, most of the world doesn't think about fuel economy (i.e. distance/volume of fuel, e.g. MPG). The rest of the world thinks about fuel consumption ( i. e. volume of fuel/distance traveled, e.g. liters/100km), and that's what's displayed on the OBC and Trip Computer. For cars that display fuel consumption, the old definition of K used on my 2014 535i makes more sense.
This whole fuel economy vs. fuel consumption is why our analog MPG displays go to infinity when we come to a stop, even though MPG when stopped is zero. The internal logic of the computer is really computing fuel consumption, and then takes the reciprocal of that value to display as fuel economy. At idle, fuel consumption (fuel volume/distance) is infinity, where fuel economy (distance/fuel economy) is zero. But, computers don't like it when you divide any number by zero. So, the needle or analog display of MPG sort of "runs home to Mama" as ST2 Jones said on the USS DALLAS in "The Hunt For Red October."