I hope an aerodynamicist chimes in on this one.
Since my experience with heat problems in mid-engined cars has only been at low (or extremely high) speeds, my logic for change-over was that at low speed, the more open LeMans style would be more effective. If some day I get to do much more high-speed than low-speed driving, it would be nice to know for sure which would be better.
Oh, and I like the look of the LeMans style much more, which didn’t hurt either.