if you work for dewan motors and are in tech - then dewan should rehire someone, The heat issue is not because of the radiator. The engine exhaust gas temp gets too high, literally cooking the engine and engine oil. The resolution is to fit a front mount intercooler with proper plumbing and a free exhaust system till the mid of the car and a dedicated oil cooler for the engine - (I dont know if the original one was air to air or water to air shared in the radiator tank) - because I have seen both kinds - Mazdas use the air to air kind though.
I have done the above mentioned works and the EGTs did drop considerably for me to put in a softer fan clutch to stop the roar the original one makes. The engine later on never got to the brink of overheating at all. Even after long runs. Not to forget our lovely owners/maintenance people forget there are 2 oil filters to change in this engine - after all its a Mazda 4 pot diesel (they are known to be robust the world over).
the intercooler sitting on top of the valve cover will only work if your engine bay has proper aimed exhaust vents. When installed on a high sitting vehicle like the sportage and the engine bay is literally open from underneath - the differential in air pressure is not that high - resulting in no air movement through the intercooler fins