As the fallout from last week’s CAFE announcement continues, worrying details about the new standards and how they appear harsher for some carmakers than others are starting to appear. The 2015 interim target of 31.6MPG fleet average for new cars and trucks is based on a complicated formula that takes into account all manner of inputs including a calculation of a vehicle’s footprint – the area bounded by the wheels – and power levels.

It’s been revealed that under the new rules the relative increase is highest for the smallest vehicles. Each automaker is assigned its own separate fuel-economy standards for cars and trucks, based on the number of vehicles of each footprint size that it sells, reports AutoWeek.

It means a carmaker like Porsche, which builds a range of small yet powerful cars, would have to average 41.3mpg in 2015. Toyota, on the other hand, which has a mix of low powered sedans and SUV models, would need to average about 7mpg less.

It’s not just Porsche that will suffer. Low volume players, with less diverse product offerings, like Volkswagen, Mercedes-Benz and BMW as well as Mitsubishi, Subaru and Suzuki, will face tougher standards under the proposal.

Porsche and a number of other carmakers lobbied hard to be exempt from the new bill but were refused. Their option now would be to either change their lineups or buy up credits and or fines from some of the larger carmakers whose fleet-average fuel-economy levels fall under the new minimum.