Length x Width x Height
EK XE360 (3x120)x120x60 = 2,592,000mm^3
EK CE420 (3x140)x140x45 = 2,646,000mm^3
so all other things being equal, the 420 in this case is slightly better even though it's thinner (45mm vs 60mm). If it was 5mm thinner it wouldn't be as good as the 360.
It's only a guide though. You won't get an accurate result (short of modelling thermodynamics with however many variable) without comparing the two side by side.
EK XE360 (3x120)x120x60 = 2,592,000mm^3
EK CE420 (3x140)x140x45 = 2,646,000mm^3
so all other things being equal, the 420 in this case is slightly better even though it's thinner (45mm vs 60mm). If it was 5mm thinner it wouldn't be as good as the 360.
It's only a guide though. You won't get an accurate result (short of modelling thermodynamics with however many variable) without comparing the two side by side.