I could weep with joy. Two different Posters referring to the radiator having 4 rows rather than 4 cores.
Anyhoo, seems to me a thin wall might suffer differential expansion and poor compression in that hole when the engine gets hot? In other words maybe the cylinder gets out of round.
On the overheating theory, I've never given this one much thought. On the surface it makes some sense. Cast iron is not a perfect conductor so thin walls will conduct more heat to the coolant than thin.
More stuff I learned in school and didn't use for 30 years. Meaning heat transfer, not engine building.