2°C and 1048 mb corresponds to an air density of 1327 grammes per cubic metre, as opposed to 1225 at ISA MSL. This is 108.3% of ISA MSL density. In other words, at ISA MSL, the density would be about 92.3% of the test conditions.
I'm not an engine performance specialist, but I would have thought that someone who is would know a correlation between intake air density and performance.