No idea what thats about, air temp does not matter beyond say, heating your cabin. All modern cars have a pseudo ‘airfoil shape’ as such cars naturally have ‘lift’. The fact that a std car weighs in at what it does, keeps it mostly on the ground. ( Some super/hyper cars DO need wings to keep the damn things planted though ). As you smooth the underside of the car you DO gain flow eff. however you also increase the lift by increasing air speed, this lowers the air pressure under the car even more… ( airfoil theory again) the more pressure differential between the upper and lower surfaces the more lift in creates. A rear diffuser, front air dam, trim plates, rear wing, spoilers are all effective ways to keep a vehicle planted. but again, 99.9% of all daily drivers do NOT need to worry about lift… ever.
Ducting… that is the key to any GOOD heat exchange system, I did a V mount for an S13 awhile back, he found that he had to tape off the std. pig nose front opening by as much as 50% because it was doing TOO good a job of cooling at hwy speeds by dropping the temps down below optimum operating temps…