At lower air temperatures the engine operates at an increased volumetric intake efficiency. I know of no lower limit to this "increased density" effect. Do you have some sort of data that shows that the increased density effect reaches a point of diminishing returns at very low temperatures?
'12 SE Sport 5Dr |╠╬╝|SGM|203a|Moonroof|17" Paint/Mach Whls|K&N 57S-4000|FFE RMM|Steeda STB, RSB|JBR bushings
'01 ZX3|╠╬╝|Pitch Blk|Prem pkg|Moonroof|SVT Snorkel|SVT Susp|Steeda STS|Z-Eng RMM|Magnaflow exh