It appears volume is somewhat accounted for: https://www.eea.europa.eu/en/analysis/indicators/co2-performance-of-new-passenger https://www.eea.europa.eu/en/anal

It appears volume is somewhat accounted for: https://www.eea.europa.eu/en/analysis/indicators/co2-performance-of-new-passenger https://www.eea.europa.eu/en/analysis/indicators/co2-perform... But only in the sense that manufacturers are pooled together to reach a certain volume and very small manufacturers are basically excluded from the regulation.