FYI, you can observe the airflow immediately aft of a front wheel well (with smooth hubcap) in this video I made to visualize the difference between "stock" and with a front wheel skirt.
It's pretty clear that adding the skirt reduces downstream turbulence.
And I think you may be right in thinking there may actually detached flow just aft of the wheel arch.
From this thread:
http://ecomodder.com/forum/showthrea...etro-5403.html