Percolation? Heat soak? Don't drive during summer??

Nope. An air cooled radiator can only achieve to much drop in temperature, the higher the air moving across it, the less heat it can remove from the coolant. An enclosed garage situation is unique and not a performance threshold of any kind.
Bullshit that's why you have a fan! The fan moves air across it! It doesn't matter where the car is! In a garage or not the fan moves air through the radiator.