I can't argue with your experience, but you are making a lot of assumptions. I have shown that in 80+ degree temps towing at 60mph the fan is 100% off and the temps climb. Once the fans are triggered the temps drop rapidly. There's a possibility a new radiator could help, and there's a possibility that the 12 year old ducting has degraded. The fact is that my 2005 F150 with a clutch fan probably has even worse air leakage and an even dustier radiator and has absolutely no issues in the same conditions because it's a truck and has a mechanical fan because obviously cooling performance shouldn't be sacrificed to try and eke out another 0.2mpg by turning the fans off on thr highway.

But that's all I know. I'm far from a "master tuner" or anything.