A scoop under the car capturing more high pressure air down there would be more effective. That is why the smallish side scoops actually work to cool the engine bay.
Contrary to belief, the X1/9 airflow is from the bottom to the top. In reality, this snorkel acted more like a chimney than an intake. In fact, at speed, it probably hurts airflow as it is pushing air in where the designed effect is to push it out.
They still look really cool though.