Typically slots in the wing are for two purposes; aiding or stalling the flow over the wings surface. How the slot creates these two very different effects depends on the slots angle to the wings surface.
To aid the airflow, you need a slot blowing nearly inline with the surface and airflow. Known as Tangential flow, this flat entry angle creates a relatively wide slot when viewed externally.
To stall the airflow, you need a slot blowing at near right angles to the surface. This creates a narrow slot when viewed externally.
Looking at what you need to aid or stall the airflow also requires different placement of the slot.
To aid the airflow, you would inject the flow from the slot in an area downstream on the wings surface where the boundary has slowed and thickened. On a front wing this would arguably be somewhere on the flap towards its trailing edge.
To stall a wing, you want to upset the airflow where it’s moving quite fast, for a front wing it would be placed towards the leading edge of the wing. Last year with F-ducts we saw the stalling slots initially placed on the flap, until Renault placed theirs on the main plane for a better stalling effect.
This analysis suggests the narrow slot towards the leading of the front wing is for stalling not aiding the airflow.