I agree with you : wind shield like hooked to the bars sounds like more drag to me : you increase S without improving Cx enough.
On the other hand, closing the air path behind the driver does not increase S but improves Cx.
I'm thinking Stiletto2 design :
But I wonder : up to 45 mph, is the SCx this influential ?
I'm thinking weight, weight distribution and rolling resistance are of paramount importance.
Also, as I understood, the potential for your top speed / acceleration is to be seeked in the controller / batteries area, right ?