[MetroMPG]

I wish I'd paid more attention to your initial planning diagram or I would have mentioned that transition sooner. I'll admit until it became "real" I didn't really look closely at it.

If you're willing to build a Kammback structure on the back of the car, I think that'll net your best drag reduction.

If not, I think adding a radius to the transition on the box lid would work.

But before fretting too much about all this, see what the tufts say! Maybe we'll be pleasantly surprised to find it's working as-is.