Coolant flow and heat dissipation works on a perculation theory. Gaskets are perforated to control flow from the rear to the front of the engine. Therefore you see a varied range of temps from rear to front. Heat has all of it's generation at the cylinder and then the coolant has to control head temps by flowing through them and theoretically keep an even base before it hits the radiator. Not perfect by any means but as the years of research between racing and everyday driven cars, the manufactures have compromised the best perculation and flow technology they can for the average applications. You will always see a cooler temp at the back and hotter in the front unless you have a weird problem.