"The ribs that extend the device do just that, they are not there to allow airflow to change its mind and swap sides after passing the leading edge. At 100 knots, how much airflow will change direction by nearly 90 degrees to passively "Blow" (supercharge) the top surface?
Wiki indeed."
Will Fraser, surely that is exactly why it happens....the higher pressure underneath creates the lift and if there is a hole anywhere then the higher pressure will bleed to the lower, regardless of speed of Aircraft or airflow.
JSP