I think what you're seeing is due to the temperature of the air being forced over the radiator not whether that air is pushed or pulled. In stock configuration the fan pulls cool (relatively speaking) air from outside over the radiator and exhausts it into the engine compartment. The VTR reverses the direction of airflow, forcing superheated air from inside the engine compartment through the radiator. The delta T between engine compartment air and the radiator is much narrower than that between outside air and the radiator. Therefore, the VTR arrangement results in less heat transfered from the water to the air and less efficient cooling than the stock set up. I suspect that's exactly the reason the engineers designed it as they did.
Once you're rolling all this changes. Now you have a supply of cooler air being introduced from the front and the fan is an active impediment to that air getting through the left radiator and while at the same time the fan is unable to draw air from the outside. The right radiator is unaffected, so the engine's still able to shed heat, but not enough because you've lost 40 to 50% of your cooling capacity. Some time back, some folks had success with a manual override to turn on the fan and also turn it OFF in exactly the situation we're talking about.