Preliminary feedback says that the double wing version of the ground effect is superior to the single version in that there is less lift so we will go down that path for now.
As for the twin fins versus the single fins I'll quote Steve Ambrose who is our man helping interpreting our data,
"The model with the central fin (compared to the model with no fin) creates a smaller increase in drag (approx. 2%) as opposed to 10% with the fins at the wheels. These increases are in the pressure drag (the drag caused by the shape of the object, not the drag incurred in the wake behind the car). Having the fins at the wheels also appears to generate lift, which is obviously not desirable, and so a clear conclusion is that the fin in the centre is better."
That is a significant difference in drag and much more than double so it is more than there just being two of them. I may try some different shapes to see if we can get it back in line but the tests are currently putting pay to this design idea.