trans cooler mounted to frame connector, Duster

I'm having a hard time figuring out why it would not work on the frame connector.

Mounted on the frame rail, fluid does not have to travel as far, so less plumbing and quicker circulation.

I would think (though I could be wrong) that there is enough air flow under the car to sufficiently cool the fins. Is there that much of a difference in airflow when the cooler is behind the grill and right in front of the radiator?

Granted there is more insulation/conduction underneath but how much makes a difference? The cooler would be mounted so as to be exposed to air.