wouldnt the thermo fan help keep the cooler air flow coming through the bonnet but?
the radiator airflow and top mount IC air flow do tend to fight against each other. hence the need for fans, especially at low speeds. how badly they fight depends on air flow down under the vehicle and how much pressure on the front side of the coolers.
font mount IC has an advantage that the airflows don't fight against each other, but the IC does block some air going through the radiator and heats it up slightly. however because airflow temp existing the IC is still far lower than radiator water temp its not a big loss.